In this paper,numerical simulations and diagnostic analyses of moist potential vorticity for a land explosive cyclone are performed.We find that the burst of the cyclone is close associated with the advection of moist potential vorticity.The development of cyclone doesn't begin at the time when a center of moist potential vorticity is above the cyclone, but at the time when the center is behind the cyclone. In addition,the existence of a distinct inverted conical subsidence zone below 200hPa is also favorable to the development.The large value zone of moist potential vorticity in lower layers has an obvious connection with activities of a lower front.The local change of moist potential vorticity connects with the magnitude of horizontal moist potential vorticity gradient.The variation of the negative/positive values of baroclinic moist potential vorticity below 850hPa is in good correspondence with the development of the cyclone.