The circulation mode of fruits and vegetables, is dominated by the wholesale markets，is the main flow pattern of Beijing at present. The wholesale markets have a strong distribution function, but they have no ability to directly face the huge number of producers and buyers of fruits and vegetables，so it can not only exist the wholesale market in the circulation processes that other main bodies of circulation will certainly join in [3] . The diagram of the model is shown in Figure 1.

This mode is based on direct procurement between powerful supermarkets and agricultural producers of fruits and vegetables through contracts. In other words, supermarkets have their own direct mining bases that reduce the circulation of links and improve the efficiency of logistics fundamentally. However, this model also has difficulties to implement: 1) Loose, small mode of production led to the difficulty of direct procurement. 2) Lack of technical guidance of crop specifications, quality and so cannot be guaranteed. 3) Traditional ways of capital settlement affect docking efficiency [4] . The

diagram of the model is shown in Figure 2.

With the continuous development of science and technology and the acceleration of the market process, the types of agricultural products, production and processing and consumption are also becoming increasingly diverse. The background of this circulation mode is some sharp carriers want to develop logistics company by integrating resources. And the logistics company will be an integrated logistics center to achieve fast and efficient distribution of agricultural products. The model is connected to the producer and terminal retailers, so it reduces the wholesale segments to improve the circulation efficiency of agricultural products, ensure freshness of agricultural products and reduce the logistics cost [5] . The diagram of the model is shown in Figure 3.

Agricultural producers and leading enterprises signed a contract and leading enterprises will buy agricultural products with slightly higher price than the market under this mode. Besides，leading enterprises will provide farmers with the information of products and technical guidance then farmers will produce and harvest in accordance with the standards set by the leading enterprises. That will reduce farmers’ risk, because farmers and leading enterprises which have the ability to control the information and bear a strong risk have signed a contract. But leading enterprises as buyer still stand in advantage, the benefits of farmers cannot be fully guaranteed [6] . The diagram of the model is shown in Figure 4.

According to the research setting evaluation indexes, science and objectivity cannot be fully guaranteed, so that the evaluation results will be affected accordingly. So the setting of index is very important especially in the case of a wide range of factors in the process of circulation of agricultural products. DEA is an analytical method commonly used in the evaluation of efficiency and productivity. It is not necessary to quantify the comprehensive input and output and determine the mathematical relationship expression between variables and determine the weight in advance. Only through the input and output data, it can effectively handle multiple input and multiple output indicators evaluation.

Setting v_i as the weight of the i-th index of x_i, u_r as the weight of the r-th output index of

y_r, so the j-th circulation patterns into integrated value is, the comprehensive value of output is [7] . Its production efficiency is defined as

So the problem is actually to determine a group of the right variables V₁, V₂, V₃ and U₁, U₂, so that the efficiency of the j-th circulation enterprise how to make efficiency value h_j maximum value. The maximum value is the value that is not likely to be higher to the other modes. Limiting all h_j values (j = 1, 2, 3) to no more than 1, max h_j ≤ 1. That is to say, to determine whether a DMU is valid need to see whether the h_k is 1. If h_k = 1, the circulation system in the circulation mode is relatively effective. If h_k < 1, the circulation system in the circulation mode is not relatively effective. According to the above analysis, it can be established to determine the relative productivity optimization model of any enterprise is as follows:

Formally, consider n circulation enterprises or DMUs that are to be evaluated, all using the same m inputs to produce p different outputs. The following table shows the input and output relations of these circulation enterprises (Table 1).

The efficiency evaluation index of each DMU is defined as:

The mode of relative efficiency optimization evaluation of the j₀-th decision making unit is:

In the above model, X_ij, Y_rj are known, v_i, u_r are variable. The model definition are weight coefficient v_i, u_r as variable, all efficiency indicator h_j of DMUs as constraint, the efficiency index of the j₀-th DMU as the goal. Whether the circulation efficiency of the j₀-th DMU is effective over other DMUs, this is a fractional programming model, which must be changed into a linear programming model to solve the problems. Making μ_r = tu_r, ω_i = tv_i, the above model is translated into:

Written in vector form as:

The dual problem is:

Written in vector mode:

The optimal solution is λ*, S*⁻, S*⁺, θ*, so we can get the following conclusions:

1) If θ* = 1, DMU_j0 is a weak DEA efficiency (overall);

2) If θ* = 1 and S*⁻ = 0, S*⁺ = 0, DMU_j0 is a DEA efficiency (overall);

3) If θ* < 1, DMU_j0 is a DEA invalid;

4) If there is a () in which holds, then economies of

scale of DMU_j0 remains same; If there is not a () in which holds

and, then economies of scale of DMU_j0 remains increasing; If there is not a () in which holds and, then econo-

mies of scale of DMU_j0 remains decreasing.

1) Material and service costs x₁ (yuan), including direct and indirect two parts.

2) Labor cost x₂ (yuan), including the discount on their own labor and the wages paid to others.

3) Land cost x₃ (yuan), including their own land rent and other collective land rent.

4) Logistics and transportation time costs x₄ (ten thousand yuan).

1) The main finished product x₅ (kg).

2) Net profit x₆ (yuan). The formula of net profit: net profit = total profit x (1-Tax rate).

3) Cost margin x₇ (%). Profit margin is the ratio of the surplus value to the total advance capital.

4) The average selling price for each 50 kg x₈.

It chooses Beijing as the object of empirical study and selects representative supermarkets, enterprises, wholesale markets, farmers market and etc as the respondents.

1) In the wholesale market as the dominant circulation mode. Beijing Xinfadi whole- sale market is DMU1, Beijing Yuegezhuang wholesale market is DMU2, Beijing Eight Mile Bridge wholesale market is DMU3.

2) “Farmer-Supermarket Direct-Purchase” as circulation mode. Carrefour supermarket is DMU4, Wal-Mart is DMU5, Hualian Supermarket is DMU6.

3) Logistics center as the main circulation mode. CMST is DMU7, Zhongdu logistics company is DMU8.

4) Leading enterprises as the dominant circulation mode. Tianan agriculture is DMU9, Material group is DMU10.

5) The circulation mode of agricultural products from the perspective of the whole industry chain. Eggplant Planting Farmers are DMU11. Survey data obtained are shown in Table 2.

The results of DEA evaluation are in Table 3.

The determination theorem of the solution of the DEA model can be known: If θ = 1 and S*⁻ = S*⁺ = 0, DMU j0 is the overall effective DEA. Table 3 shows that DMU4 and DMU11 are the overall effective DEA in 11 DMUs, others are invalid DMUs. So the output and input of DMU4 and DMU11 will reach the maximum value.

From the output of the θ value can be seen five circulation modes of the highest efficiency is the circulation mode of the fruits and vegetables from the perspective of the whole industry chain.