This paper used frequenity to analyses natural flow of wet and dry years in four areas of Chang Jiang, Huai He, Huang He and Hai-Luan He. The subordinative measure of wet and dry years of each station and fuzzy probablity of encounter of wet and dry years among the stations were calculated by fuzzy mathematical method. Acceding to analyses of the results, these are proved to be true that encounter of wet and dry years in Chang Jiang and Hai-Luan He is random and the most in Chang Jiang, Huai He and Huang He are the same time.The water transfer area is considered as one hand, and water recieve areas as the other hand. The encounter of wet and dry years in water transfer and water receive areas of eveiy routes of southto-north water transfer is calculated considering effects of through region on it. According to the encounter of wet and dry years, the middle route (on the middle reaches of Han Jiang) is better. Finally, we analysesed the frequenity neartude of wet and dry years, approved the results of fuzzy probability of calculated.