Based on the routine observational data and the result of the Mesoscale Model (MM5V3.7) simulation, the cause of snowstorm process in northeast of china in Ma r.35, 2007 was analyzed. The results indicate that vertical shear of upper and lower air and strong ascending caused by upper air divergence and lower air con vergence, as well as the generation and maintenance of midlower air positive v orticity are the dynamical mechanism, and the cold and dry air invasion is the t rigger factor. Profuse water vapor from East Sea and South Sea with northward ai rflow from south at east of cyclone is the important reason of snowstorm.