This paper diagnoses and analyses in detail an explosive cyclone that occurred on West Pacific, and investigates its developmental mechanism based on potential vorticity inversion of frontogenesis diagnosis method, which synthesizes Etter potential vorticity inversion diagnosis and frontogenesis function diagnosis. It shows that the project of diagnosis and calculation in this paper has a great deal of maturity and rationality after verifying the effect of the contrast results which are calculated from the project of potential vorticity inversion of frontogenesis diagnosis. And it also shows that the effect calculated is competent for the demand of diagnoses and analyses in reality. This paper firstly analyses and discusses in detail the potential vorticity evolvement characters of the explosive cyclone in the course of its formation and development, and then based on this diagnoses quantitatively investigates the action and affection of the upper,middle and lower level potential vorticity disturbances and unbalance wind during the different stages of the cyclone’s life cycle.The upper level potential vorticity disturbance is in contact with the troposphere enfoldment phenomenon, the middle one results from the condensation latent heat release ,and the lower one represents the frontal zone disturbance. The horizontal convergence and divergence is main component of unbalanced wind, and this paper also analyses and discusses the interaction between them and the mechanism of the cyclone's explosive development.