The agricultural drought disaster was analyzed by using risk analysis model and risk hierarchy of information diffusion theory based on the statistical data of oasis agricultural drought stricken area, disaster area in the middle and upper Heihe River each county during 1991—2010. The results showed that the probability of drought risk on agriculture decrease with the increase of risk level in the researched area in recent 20 years. When the drought stricken index was within 50%, the estimated value of the disaster stricken risk reached minimum in Linze (0.000 29) and reached maximum in Shandan (0.811 12), equivalent to 1.2a occurrence. When the drought forming index was within 30%, the estimated value of the disaster forming risk reached maximum in Shandan (0.765 50), equivalent to 1.3a occurrence; while it reached minimum in Ganzhou (0.118 95) and drought occurred almost every year. Drought occurred in high concentration and frequency, most of the losses were within 15% but the losses with degree more than 30% are of little possibility. When the drought stricken and forming index was at 10%, the losses with degree reached maximum in Gaotai, Minle and Shandan, but the losses with degree more than 50% are of little possibility. The risk probability of agricultural drought had a significant spatial difference. It showed that Ganzhou and Linze as the center, the drought risk level gradually increases to the periphery. The highest risk level of drought was in Shandan and Minle, with a high and higher risk levels. The lowest risk level of drought was in Ganzhou and Linze, with a low and lower risk ranks levels.