Abstract: In this paper,the results of experiment of dynamic extended-range forecasts (DERF)with T42L9 model for dekad and monthly mean circulation during the summer heavy rainfall period in 1991 over the Yangtze and Huaihe River Valley and the sensitive experiment of thermo-dynamic effect of the Qinghai-Xizang Plateau on the circulation anomaly are Presented.It has been shown that DERF method with T42L9 model has some ability for prediction of mean circulation anomaly including the summer heavy rainfall,and the plateau,s thermo-dynamic anomalous effect may be an important factor for the persistent rainfall process.