Abstract:Based on the observation data and NCEP (1°×1°)6 h reanalysis data, the synop tic dynamic analysis of the snowstorm process in Xizang Plateau in October 2005 was made. The result shows that several factors have play important roles in the snowstorm process as follows: the instable atmospheric stratification fo rmed by the co action of upward moist airflow and downward cold airflow at the up level, the pumping effect of the divergence at upper level and the specific t errain of Xizang Plateau. Bay of Bengal and South China sea are the sources of th e vapor of the snowstorm. The vapor is transported to the Xizang Plateau throug h two passages. The vertical profile of helicity, with positive and negative hel icities respectively in the low and upper level over snowstorm area, and the exc eptional area of moist potential vorticity are both closely related to the snows torm.