Seasonal drought has serious affections on agricultural production in Hunan Province, Developing an optimal cropping system to prevent and avoid drought disaster could provide scientific guidance for local agriculture production. In this study, adaptation and ensure index between precipitation and crop water requirement were analyzed using weather and crop phenological data of representative stations in Hunan Province from 1981 to 2007. Then optimal cropping systems based on precipitation were evaluated for the local agriculture to prevent and avoid local seasonal drought. Representative stations and cropping systems were selected according to the aridity and topography. And crop coefficients used in the study were amended using the time-averaged single-value approach recommended by FAO. Results showed that: (1) the optimal cropping systems were wheat-rice and potato-rice in humid low-altitude complex-terrain area of north Hunan Province and sub-humid medium-low altitude hilly area of northeast Hunan Province,(2) while in sub-humid low-altitude plains area of north Hunan Province, it was more suitable to adopt cropping systems of rape-cotton rape-rice and soybean-rice, (3) in sub-arid low-altitude plains and hilly transitional area of east Hunan Province, optimized cropping systems were rape-sweet potato, rape-cotton and rape-rice Similarly, for the other areas, it was,(4) rape-rice, wheat-rice and potato-rice in arid low-altitude hilly area of southeast Hunan Province, (5) rape-rice and rape-cotton in arid low-altitude basin area of middle-south Hunan Province, (6) potato-rice and rape-sweet potato in the humid high-altitude hilly area of northwest Hunan Province, (7) rape-sweet potato, rape-rice, wheat-rice and potato-rice in humid high-altitude hilly area of southwest Hunan Province, (8) and rape-sweet potato and rape-cotton in arid high-altitude hilly area of west Hunan Province.