The surpass probability of precipitation of different levels during the singlecropping rice growth period in Zhejiang Province is studied using the risk assessment model based on the principle of information spread by means of the precipitation data during the singlecropping rice growth periods from 58 local meteorological stations from 1971 to 2004. With the risk charts of differentlevel precipitation, the risks of droughts and floods for singlecropping rice and their damage to rice yields are evaluated. The results indicate that the highrisk areas with precipitation lower than 400 mm are located in the coastal island areas, Jiaxing, and the JinhuaQuzhou basin, where rice suffers heavier drought damage. The highrisk areas with precipitation higher than 1000 mm are found in the southeastern coastal areas (including Linhai, Wencheng, Wenling, Ninghai, Taishun, etc), where singlecropping rice suffers greater flood damage (typhoon rainstorm). Compared to the drought disasters, which may be relieved by irrigation, floods have greater contribution to rice yield reduction.