The characteristic of climate variability of tropical cyclone activities in Northwest Pacific Ocean is studied by using Besttrack data (1950-2001) of JTWC. Proper factors to describe tropical cyclone activity, including genesis location, frequency and track, are selected and series are formed firstly. Variance analysis and wavelet analysis are applied to the series. Results show:1.Interannual variation of tropical cyclone activities in Northwest Pacific Ocean is evident, the main change periods of series are during 2-4 years; 2.By using wavelet filter technique, inter-decadal variation of tropical cyclone activities in Northwest Pacific Ocean is revealed, and characteristic of interannual variation in different phases of inter-decadal variation are quite distinct;3. Tropical cyclone activity in South China Sea is unique in Northwest Pacific Ocean from wavelet spectrum results.