Abstract: Synoptic and dynamic conditions of a severe convective storm occurring in the plain of North China on 21 June 1998 were investigated. It was favorable for the occurrence of the storm. In addition, a warm-dry cover and the differential temperature advection between mid- and low- troposphere are quite important to the formation and development of convective instability, and to the accumulation of convective available potential energy as well. The genesis of convective clouds was triggered by the turbulence of westerly in the mid- to low-troposphere. Moreover, the convective clouds kept on developing during their process moving rightward. Such phenomenon was relevant to dynamic pressure vertical acceleration locating to the south of convective clouds, the import of the warm-wet air and the clouds combination.