Seasonal operational forecast dataset of summer precipitation (1978-2008) was used to investigate the forecast ability and forecast skill. Compared with 160 stations’ observations (1951-2008), the high forecast skill years and the low forecast skill years were distinguished. The highest forecast skill appeared in the years when dry domain controls the Yangtze-Huaihe River Basin; however, the lowest score appeared in the years when the mid-low Yangtze River Basin was wet. Two signals from inter-decadal and interannual timescales should be utilized in the operational forecast. For the interdecadal timescale, the monsoon region in East China should be divided into several sub-regions first, and then actual inter-decadal signals at individual sub-region can be used in the operational forecast. Inter-annual precursory signals could be the biennial oscillation and seasonal forcing such as the sea temperature, snow cover and soil moisture anomalies.