Based on daily precipitation data from 1951 to 2014 in Nanjing,NCEP/NCAR daily reanalysis data,and NOAA monthly Extended Reconstructed Sea Surface Temperature data,the pentad evolution characteristics of summer precipitation in Nanjing and its associated anomalous circulation are analyzed using empirical orthogonal function(EOF) decomposition,wavelet analysis,composite analysis,and regression analysis.Results show that summer precipitation in Nanjing is concentrated between the 5th pentad of June and the 3rd pentad of July,and mean precipitation intensity during this period is 8.2 mm·d^-1.Nevertheless,mean precipitation intensity between the 1st and 3rd pentad of June and between the 4th pentad of July and the 6th pentad of August are only 4 mm·d^-1 and 4.5 mm·d^-1,respectively.Precipitation intensity shows a “double-peak” structure in the climatology,with the peak time occurring in the 5th pentad of June and the 1st pentad of July,with the precipitation intensity in these two pentads both reaching 9.4 mm·d^-1.The wavelet analysis results show that the precipitation peak time also has a decadal variation of ～10 years.The pentad evolution characteristics of precipitation shows a conversion between three states—a “single-peak” structure with the peak time occurring in the 5th pentad of June,a “single-peak” structure with the peak time occurring in the 2nd pentad of July,and a “double-peak” structure—in different years.Regression analysis of atmospheric data demonstrates that it is the atmospheric circulation anomalies that lead to the “single-peak” structure of precipitation.When precipitation's “single-peak” occurs in the 2nd pentad of July(5th pentad of June),the western Pacific subtropical high(WPSH) tends to be weak(strong) and eastward(westward),the East Asia trough and Baikal shallow trough tend to be weak(strong),the vapor in the lower troposphere around Nanjing tends to be anomalously divergent(convergent),and the vertical velocity in the middle troposphere tends to be downward(upward);and this kind of anomalous atmospheric circulation pattern is(is not) conducive to the formation of precipitation,such that the precipitation intensity is anomalously weak(strong) in the 5th pentad of June.On the contrary,in the 1st and 2nd pentad of July,the WPSH tends to be strong(weak) and westward(eastward),the East Asia trough and Baikal shallow trough tend to be strong(weak),the vapor in the lower troposphere around Nanjing tends to be abnormally convergent(divergent),and the vertical velocity in the middle troposphere tends to be upward(downward);and this kind of anomalous atmospheric circulation pattern is(is not) conducive to the formation of precipitation,such that the precipitation intensity is anomalously strong(weak) in the 1st and 2nd pentad of July.The preceding winter sea surface temperature(SST) anomalies of(10°—20°N,175°E—150°W) show significant correlation with the variability of the precipitation peak time—the summer precipitation in Nanjing tends to show a “single-peak” structure with the peak time occurring in the 2nd pentad of July(5th pentad of June) when the preceding winter SST of this sea area is anomalously warm(cold)—such that the preceding winter SST anomalies of this sea area can serve as a forecasting factor for summer precipitation peak time anomalies in Nanjing.