Using routine weather maps of west hemisphere and daily precipitation data of New York from 1980 to 1990,extratropical cyclone in North America has been classified as three types. The climatic features, process of formation of three types and its influence on rainfall of New York have been analysed. The results show that the mean frequency of extratropical cyclone during winter time is fifty-one,its annual chang is small;Cyclone number is twelve in maximum month, five in minimum month,the distribution on time of three types of cyclones and their affection on precipitation of New York are different.