Abstract: Before forecasting the frequency of the tropical cyclones affecting East China in the flood season by using statistical interpretation forecasting method, a series of earlier stage researches are made. It’s found that: (1) Abnormal frequency variation of the tropical cyclone affecting East China is caused by the adjustment of mean monthly circulation of the Northern Hemisphere in flood season; (2) The long wave reflecting the characteristics of mean monthly circulation has a good relation to the abnormal frequency variation, especially in abnormal years the weather system and the correlation area are stable; (3) Using the correlation analysis the statistical forecast equation for the frequency variation of the tropical cyclone is set up. Based on the correct short-range numerical forecast for climatic situation the accuracy is about 70% using statistical interpretation forecast method, and if the abnormal variation of mean monthly circulation could be predicted, the trend of abnormal frequency variation could be predicted.