The Mesoscale Convective Systems(MCS) in the coastal areas of South China during 16th-17th July 2006 was simulated using mesoscale numerical model WRF(weather research and forecasting model),and we analyzed the precipitation process combining with observation data.The results show that:1)The activity of MCS was closely related to the remnant of the downgraded severe tropical storm "Bilis" and southwest monsoon.The tropical depression provided dynamic conditions for MCS and southwest monsoon brought plenty of aqueous vapor to South China,the continued combination of tropical depression and southwest monsoon caused the formation and development of MCS;2) The MCS has an obvious asymmetry structure,the upper cloud stretched to south and the nephsystem distributed in a northeast-southwest band and mainly located in the south of tropical depression;3) Using WRF model to simulate the heavy rain process produced good results,which represented the development of MCS and the distribution of rain band;4) The cloud water content was little and ice crystal content was large in the mesoscale convictive cloud cluster,so ice crystal precipitation mechanism was the main precipitation mechanism.