Based on the satellite imagery and Meteorological Observation, a mesoscale vortex over North China on 17 July 2002 is analyzed. The results show that (1) The Vortex formed in weak baroclinic front zone, and caused by the interaction of muti scale disturbance of mutil cells. (2) The vortex was a shallow system, there was only a convergence area in 850hPa. (3) Without external vapour resource, the vortex weather was mainly high wind and hail. The energy released while it accumulated during the formation of vortex.