With the NCEP reanalysis data, the CMA tropical cyclone data and the Scripps temperature data, the climatic background of interdecadal and interannual abnormal year for typhoons in western North Pacfic was analyzed. It is shown that the interdecadal change in the frequency of typhoons is related to the subtropical high and the SST change of the thermocline in the western equatorial Pacific.The interannual change has a close harmonic connection with the subtropical high, monsoon trough, the crossequatorial flow and the SST change of the mixing layer in the eastern and middle equatorial Pacific.