Based on the conventional and nonconventional observations, reanalysis data, P WV potential water vapor data, and satellite images, the convective rainstorm oc curried in Shanghai on 25th Aug, 2008 is analyzed. The results show that a sub synoptic vorte x is developed by three strengthening flows from South China, over sea and highe r latitude area, respectively, which can explain the convergence of moisture tra nsportation, the accumulation of high energy in previous 12-24 hours, and th e trigger of vertical velocity and energy release. A series of satellite picture show the merging of cloud clusters to induce a burst of precipitation. A nd the slow movement could partly explain the significant accumulation of rainfall in a short time. GPS/PW V images display the enriching process of moisture.