Study on a new method of crop yield forecast

The meaning of the tendency yield was defined by analysing the characteristics of tendency of summer and autumn grain crops in Gansu Province. Base on this a concept of the fluctuant rang of yield was given. The fluctuant rang is made by the lines of the highest yield and lowest yield. Reality yield moves surrounding the tendency yield in the fluctuant rang of yield. Concrete methods for forecast has been given, which not only decreases the extent of result of yield forecast but also improves the accuracy of yield forecast by confining yield change in this narrow rang.