Abstract: Oasis agriculture is the essence of agriculture in arid areas of northwest China. With the double constraints of scarce natural endowment and fragile ecological environment,the high production efficiency of low investment and high yield is an important way to crack the double limits. Therefore,it is very necessary to evaluate the production efficiency,analyze its influence factors and further put forward the improvement strategies. However,due to the availability of data,the current evaluation of agricultural efficiency is often limited to the macro-regional level and lacks micro-level research. Farmer is the most basic agricultural production units,therefore, to evaluate the production efficiency,summarize the representative area of the oasis agriculture efficiency,and put forward the corresponding improvement measures and policy suggestions from a micro operational level of the farmers' input and output undoubtedly has better operability. Middle Zhangye in Heihe Basin has been developing agriculture since the ancient times,it is a typical representative of the northwest arid oasis agriculture,and the biggest seed corn production base in China. Based on input-output survey statistics of Zhangye,this paper supplemented special surveys. Taking seed corn farmers as the research object,this paper first evaluated the production efficiency of seed corn farms,and analyzed the regional factor and scale factor for the efficiency differences,by using data envelopment analysis(DEA)evaluation method. Results show that the regional average production efficiency was 0.863 3,and the production efficiencies differed at different scales of farmland:production efficiency was up to 0.934 0 in small farmland,0.847 6 in middle-scale farmland,and 0.828 9 in large-scale farmland. Then,based on the results of the CCR model based on input angle,the target value of input elements was used to replace the initial value to reevaluate the efficiency value,finally,the improved percentage of efficiency value were calculated by comparing the improved simulated efficiency value with the initial efficiency value. Results show that for small-scale farmers,enhancement of different input elements to the production efficiency was generally equal,with an average value of about 6%;for the medium scale and large-scale agricultural farmers,the reduction in planting area contributed the most to the increase of production efficiency,which were 12.76% and 15.38%,respectively. Suggestions are:establishing regular efficiency assessment measures,adjusting the planting scale according to the current scale of production,strengthening the infrastructure construction,adjusting cropping system,and improving the utilization efficiency of elements.

Key words: farmer's production efficiency, seed corn, DEA model, economies of scale