The snow-storm in the eastern part of Qinghai Plateau during 21-22,October 2002 was the heaviest process in the last 10 autumns. Based on infrared imagery,vapor image and some conventional observation,the synoptic diagnostic analysis of the snow-storm is made. The results show that there is a good corresponding relationship between Q-vector moist frontolysis function,Q-vector divergence,vapor flux divergence and the snow-storm region of the Qinghai Plateau,and this has a good implication for the snowfall forecast in the Qinghai Plateau.