A rainstorm process in north Shaanxi on 27 July 2012 is studied by using the 1°×1° NCEP/NCAR reanalysis data,observed surface precipitation data and black-body temperature(TBB) data from FY-2E satellite.The rainstorm process is simulated by WRF(Weather Research Forecasting) mesoscale numerical model and diagnostic analysis is made by using WRF model outputs.Results show that the rainstorm took place in regions between the northwest marginal zone of the western Pacific subtropical high and the Baikal cyclone.In the middle and low layers,the water vapor originated from the Bay of Bengal,passed the eastern Tibetan Plateau and arrived in north Shaanxi.The process from the small non-organized cloud clusters to self-organized cloud clusters stimulated the development of mesoscale convection system.Near the trough line,the mesoscale gravity wave could be caused by geostrophic adjustment in the right of jet stream exit region at 200 hPa.The energy of downward propagation of mesoscale gravity wave was absorbed by the atmospheric neutral layer near surface,which leaded to the convection development in lower atmosphere layer,and promoted the genesis and development of rainstorm.