In order to study the interception law of forest canopy to precipitation, based on the theory of stored-full runoff in watershed, a new model of precipitation interception was developed from mechanism of forest canopy intercepting rainfall. The determining method of model parameters was produced by combining with observation data of two woodlands. The effectiveness of the model was also examined. The results showed that calculation values well fit observation values well. Therefore, the model revealed a general law and characteristics of forest canopy interception to rainfall. This model could be applied to forecast calculation of interception when model parameters are given.