Abstract: In the arid and semi-arid areas of middle part of Kansu province, the main meteorological factors affecting crop yield are precipitation and evaporation. This paper discussed the relationship between the meteorological factors and the yield of spring wheat of Dingxi Area, and worked out a mathematical model: ŷ=w1ŷ1+w2ŷ2. The accuracy of the model has been tested according to a vast amount of historical data. The scope of application of the model has been discussed. We have predicted successfully the yield of spring wheat got in 1982.