Abstract: In reviewing both the observed and predicted summer rainfall in China in 2010, the authors have proposed a judgment that the lack of external forcing factors such as pre-winter sea temperature and snow when using the objective and quantitative prediction method of summer precipitation based on changeable configuration of optimal multi-factors may lead to forecast failure in some regions. Through the diagnostic analysis of possible climate causes of abnormal summer precipitation combined with the results of hindcast, the authors have verified this judgment. In addition, abnormality occurs in varying degrees within each member of Asian summer monsoon system in the context of pre-winter sea temperature and snow anomalies, and the western Pacific subtropical high is the most significant, which mainly induces the abnormal summer precipitation. At last, the authors put forth the possible ways to improve this prediction method.