he mesoscale structure and development reasons for a loc al storm in Beijing on 10 July 2004 are investigated by using the mesoscale num erical simulation. The results indicate that the MCS are the mesoscale convergence line and low pressure system in the mid and lowlevel, with the convergence in the low level, divergence in the high level and strong ascending motion during the strong development stage. Before the heavy rain, the surface sensible and la tent heat fluxes resulted in the temperature increase, pressure decrease and the water vapor accumulation, which influenced the wind distribution and played an i mportant role on the formation and development of the local storm.