Abstract:A successive snow storm appeared on January 18 to 19, 2006 is analyzed. It shows that this case is different from the samples in the past：（1）The pol ar vortex at high level is stable and its intensity is large, polar front locate d at more north than the normal. The short wave trough split from the polar fron t overlapped with the south trough and made it develop and deepen. At that time, the snow storm occurred. (2) On the surface, reflux in the southeast and invert trough near the Hetao area jointed together and met with cold air from the nort h and caused the snow storm. （3）The deep moisture layer and the strong water vapor convergence together offered plentiful water for the snow storm. The center of the snow storm located at the south of two water vapor flux axes at low and mid level separately. (4) The vertical allocation of the divergence at upper and convergence at low level,the strong ascending motion and dew point front continually lifting action triggered greatl y convective and uns table energy to release at the mid level and it is an important mechanism of ca u sing successive snow storm. But LLJ and super LLJ can not only offer source of water vapor and transportation of energy but also make gravity wave develop unst ably, and that i s another important triggering mechanism of snow storm. (5) The snow storm appe ared at the right and before maximal advection center of the vortex at 500hPa. A fte r 12 hours, the intensity of the positive vortex advection center increased r apidly when there is an increasing rainfall.