In order to describe quantitatively the relation between subtropical high variation and summer precipitation in Jixing, a subtropicalhigh index is defined by selecting a specified key area on 500 hPa. The analysis of the index indicates that there existed very good relation between subtropicalhigh index and summer precipitation with interdecadal variation periods of more than 45 years and about 9 to 16 years, as well 4 years and quasi2 years. The index can be used in operational precipitation forecasting. There occurred a synchronous interdecadal jump in summer precipitation in Jiaxing and Northwest Pacific Ocean tropical high around 1980. Before 1980, the tropical high intensity was weaker and farther eastern than normal, while the precipitation in Jiaxing was less than normal; and after 1980, vice versa.