Abstract: Tropical cyclones which rapidly intensify (ΔV≥20m/s in 24th) in the Northwest Pacific Ocean west of 135°E could have adverse influence on oceanic and coastal economic activities in China,71% of which landing in China. Rapid intensification are mostly seen east and northeast of Luzon Island.It was much correlated with sea surface temperature(≥28℃) and upper air conditions,such as enhanced subtropical high, onset of Southwest monsoon surge,insertion of modest cold air,and Tropical Upper Tropospheric Trough (TUTT) et al.Above mentioned processes enhance inflows in the low level and deep convection in the upper level.Statistics of satellite pixels have also shown that rapidly intensifying tropical cyclones are marked by a sharp increase in the inner core convection and stable or slowly increasing deep convection in outer region.Non-rapidly intensifying tropical cyclones have only constant or decreased deep convection in inner core and outer level.The sharp increasing of deep convection in the inner core is a forewarning of rapid intensification of tropical cyclones.