Abstract: The influence of thermal states in the warm pool on tropical cyclones (TCs) in west North Pacific is investigated. There are fewer typhoons during warm years of the warm pool in which tropical storms tend to form in the northwest quadrant and move westward. Inversely, the number of typhoons, which tend to recurve northeastward to the southeast of Japan, increases in the southeast quadrant during cold years. Based on a composite analysis, the circulation-induced dynamic factors rather than thermal factors are identified as responsible for TCs activities. During the warm state, the monsoon trough retreats westwards, which leads to anomalous vorticity in low-level and divergence in high-level in the western part of west Pacific. Above-normal TCs activity is found in this area. Furthermore, wind anomalies in 500 hPa determine the main track types. On the contrary, when the warm pool is in cold state, the atmospheric circulation is related to the formation of more TCs in the southeast quadrant. There are easterly shear in the south and westerly shear in the north of northwest Pacific, which is favorable for tropical cyclone development.