Due to the enormous disaster caused by the heavy rainfall in Henan and Anhui on 9 July 2005,the process is simulated by using mesoscale model(MM5) and is studied based on NCEP／NCAR reanalysis data and product of MM5.The results show that the Baikal blocking,cold vortex over Northeastern China and the highlevel trough were propitious to the heavy rainfall.The lowlevel jet and shear were the main systems leading to the rainfall.According to the change of divergence,vorticity,vertical velocity,helicity and equivalent potential temperature,it is obviously found that atmosphere converged and ascended,and lowmidlevel stratification instability was very apparent in heavy rainfall area.Additionally,uplowlevel matter exchange was intense.The vertical profile of helicity over heavy rainstorm area was positive in the lowmiddlelevel and negative in upperlevel of troposphere.The large positive helicity area corresponded to the center of the rainstorm.Distribution of moist flux divergence presented that there was strong moisture convergence in the rainstorm area.Moreover,frontogenetic condition provided energy and vapor for the rainfall and its reinforcement.