Abstract: The causes of an abrupt mesoscale heavy snow process in Dandong region on Dec.6th,2004 were analyzed in this paper.The results showed that the occurrence of heavy snow had a close relationship with the mesoscale coastal front and the cold front at the synoptic scale.The mesoscale coastal front would be strengthened under advantageous synoptic scale systems and would move toward the inland.The main reason resulting in an abrupt mesoscale heavy snow was the superposition of the lower clouds arising from the mesoscale circulation over the mesoscale coastal front and the cold front clouds.