Abstract: In this paper，it is described that utilizing the advantage of grey sys-tem theory and taking the data of precipitation from 1941 to 1986（46 years） in Urumqi area，a set of grey mobile state model was developed and the future 21 years＇precipitation tendency was studied．It was verified by the data of precipitation from 1981 to 1986 years in Urumqi area．An ideal re-sult has been obtained．And the scientific bases were offered for forecasting grain output and working out agricultural plan．