Abstract: Using a improved model of MM4, the genesis and development of the mesoscale systems with the heavy rainfall are further discussed based on the three typical heavy rainfall events (81.7, 81.8 and 91.7) in China. The principal findings are: It is important to the mesoscale systems that a cyclonic vorticity is generated and developed within an unstable and warm air with moist, while a persistently intensive ascending motion is maintained with whole vorticity column. The effect of the condensation latent release on the mesoscale systems development is significant. The various physical processes, model parameterization, the configulation of the Qinghai-Xizang Plateau forming the external forcing influence and the model spatial resolution and so on are all important to the simulative results concerning the structure, evolution and precipitation for the mesoscale systems producing heavy rainfall.