Abstract: Using the output data of an MM4 mesoscale numerical model which fairly well simulated the developing structure and the evolution of the "96.1" snow storm event over the Qinghai-Xizang Plateau, a nonlinear transversal wave instability model and simulation system is developed to validate the formation mechanism of the snow storm process. The results show that the fields of vertical velocity are coincident with not only with those of the stream function, but also with the observations. It indicates that the transversal wave instability is substantially a formation mechanism for the occurrence of the "96.1" snow storm.