Taking Wulanchabumeng as an example, on the basis of the relative variation of per unit area potato yields from 1961 to 2000, using such indexes as the yield reduction rate, the yield reduction rate variation coefficient, the yield reduction rate probability and synoptic risk as evaluation stands, the risk distribution regularity of per unit area potato yields in Wulanchabumeng is analyzed by means of the small grid resource deduction method. According to the climate similarity theory, using the optimal dynamic cluster method, the risk compartment of potato plating is given. At the same time, factors that affect the potato yields are also analyzed. Results show that droughts either in spring, summer or all the year round, as well as big precipitation variations, are main reasons that cause potato yield fluctuation in the area.