Abstract: A diagnostic analysis of two explosive cyclogenesis and a general cyclone over the Northwest Pacific Ocean in 1979 is made by using both potential vorticity and E-P flux. The analysis results demonstrate that explosive cyclogenesis development is caused by the concentrated condensation heating resulted from abnormal stratospheric potential vorticity and tropospheric turbulence. The main dynamic mechanism is upper-level forcing and middle-tropospheric aqueous vapor transportation, which result in large-scale convergence condensation latent heating.