The mesoscale numerical model MM5(V3) was used to simulate a heavy rain process on a Meiyu front in the Jianghuai area during the period from 2000BST July 4 to 2000BST July 5, 2003.The high spatial and temporal resolution model outputs were used to diagnose the dry intrusion and its effect on the heavy rain process.The results show that the dry intrusion play an important role in the development of the heavy rain process,and the dry air with high potential vorticity in the upper troposphere intruded into the lower layer,which promoted the development of cyclone and convection,and subsequently the enhancement of precipitation.