The monthly meteorological data from 1960 to 2012 in 8 stations in Sichuan agricultural regions was used to calculate the precipitation satisfied degree, and the grain production and reduction due to drought in Sichuan from 1988 to 2007 was used to calculate the grain reduction rate in “wheat-rice” and “wheat-corn-sweet potato” cropping systems respectively. The drought risk probability of the precipitation satisfied degree was calculated by normal distribution function, and of the grain reduction rate due to drought was studied by information diffuse theory. The results showed that under the two cropping systems precipitation can’t satisfy the crop water requirement in one year every five years in most agricultural regions of Sichuan province, so the irrigation is needed. In “wheat-rice” and “wheat-corn-sweet potato”, the probability of medium drought, heavy drought and severe drought is 39.7%、10.9%、4.9% and 32.7%、6.1%、3.2%, respectively. The precipitation satisfied degree is well related with the grain reduction rate. When the grain reduction rate indicated medium or heavy drought, the precipitation satisfied degree anomaly must indicate the occurrence of drought. However, when the precipitation satisfied degree anomaly indicated the occurrence of drought, the grain reduction rate did not necessarily judge the medium or heavy drought.
