Tropical Cyclone (TC) and typhoon is one of the severe and abrupt natural disasters. In recent 20 years, the research on TC and typhoon climatology has become one significant aspect of TC field and made great progress. Reviewing the previous studies of the TC variation on time scales longer than season, this paper presents major mechanisms which modify the variation of TC and typhoon activity in the western North Pacific(WNP). These mechanisms involve low frequency oscillation, monsoon trough and west-propagating equatorial waves, ENSO and QBO, which alter the circulation feature and thermal structure in WNP. Based on the latest research progress and author's study results on TC and typhoon climatology, the prospect in this field and some further consideration of the scientific problems, including energy exchange in monsoon trough, dynamics processes in difference area, evolution of equtorial waves and TC prediction on time scales longer than season are proposed.