Abstract: The hydrological partitioning is not only governed by the relative magnitude of precipitation and potential evapotranspiration (PET), but also by their seasonal distribution. Based on the daily observations from 743 national meteorological stations during 1956 to 2010, the FAO-Penman equation was employed to calculate daily PET. To construct the seasonality indices, the interpolated 10-km grid daily precipitation and PET were analyzed. The results indicate that the daily PET shows an overall decreasing trend over 82.8% of the China, while the decreasing rate is not large. And the other seasonal indices of PET also have no significant trend. As for precipitation, the seasonality index has a significant decreasing trend across the China with a largest rate of 6.4% per 10 years in northwestern regions and the decreasing trend is more severe in northern basins. The centroid and duration of precipitation regime have not shown obvious changing pattern. The changes in precipitation and PET seasonality can lead to decreasing runoff, which should be noted in the future research on the attribution of change in runoff.