Abstract: In order to figure out the problem of summer rainstorm false forecast, we used the data from conventional meteorological observation, FY-2D meteorological satellite, radar, automatic weather stations and NECP reanalysis, to analyze two processes with great differences in precipitations in a similar circulation background in July, 2012. The results showed that the main reasons of great differences in two precipitations were the system configuration of upstream and downstream and generation of meso- scale system under the background of similar large scale circulation. On July 6, the cold air weakened while the short wave trough moving eastward, at the same time the dynamic conditions of precipitation, water vapor and instability conditions weakened, shower appeared in south central Shanxi. On July 8, the cold air strengthened while moving eastward, the height and wind fields showed apparent ageostrophic characteristics. Meso-scale shear line, jet stream and vortex were generated, the water vapor transport and convergence that influencing the precipitation strengthened, the convection developed, which leaded the emergence of regional rainstorm weather in south central Shanxi. Therefore, in a similar circulation background, the numerical weather forecasting products should be revised by analyzing the evolution of the upstream and downstream system, and the upper and lower configuration of the meteorological elements fields to reduce rainstorm false forecast.