Abstract: The heavy-hard rain in northeast QinghaiXizang plateau means rainfall ≥25.0 mm in 24 hours. The regional one means that there are, at least, three stations rainfall each ≥25.0 mm in 24 hours. Diagnoses and numeric simulation were made on a heavy-hard rain in the Northeast Qinghai-Xizang Plateau during 29-30 July 2003 using NCEP data of 1°×1° with 6 h intervals, observed data and MM5 model, to get the synoptic situation, configure of physical and evolvement characters of satellite cloud picture and the influence of the complex topography over the northeast QinghaiXizang Plateau. The results show that the circulation pattern of the rainstorm is meridional cell of tworidge one trough and the west secondary model of South Asia High. The main impact systems are westerly trough and low vortex.The main characteristics of satellite cloud picture for this regional heavy rain is overlapping of the different cloud systems, which reflect special weather systems. One of reasons, which lead to heavy-hard rain during the overlapping, is that the overlapping leads to unstable development of the inertialgravity waves. The overlapping can offer the important gist for the rainstorm forecast over plateau and its vicinity.MM5 can simulate this heavyhard rain's precipitation life and the trend of distributing of timevariation and can provide the highresolution data to diagnose rainstorm in plateau.The original vapor source of rainstorm in plateau is not from the coastal area, but from land to form sublevel and multilevel. The cause of heavy rain in this area is convergence in the low level and intensity of cyclonic vorticity and strong upward motion. The Ω field of θsein the low level is kind of unstable stratification and the rain belt present to warm tongue. The topography in northeast QinghaiXizang Plateau is very complex. The process which are river shape topography in northeast plateau and the mesoscale one piling on the plateau impacting on the cold and warm flow is very important for the heavy-hard rain, and the main .