Based on the objective analysis data of NCEP FNL and theprecipitation data from China’s automatic station and CMORPH,this paper carried out a synoptic background analysis of a heavy precipitation process in Shanghai from August 23 to 24,2015.A quantitative analysis of the specific impact of the 1515 typhoon known as "Typhoon Swan" on this precipitation process was conducted by means of the potential vorticity inversion method,so as to explore the mechanism of the rainstorm process,and the following main conclusions were drawn:1) The method of vorticity inversion is able to accurately reflect the characteristics of the westerly trough,typhoon and sub-tropical high pressure and other important weather systems,and can effectively reproduce the evolution of these systems;2) The main cause of this precipitation process was the intersection of north cold air and northeast air flow over the long-distance typhoon;3) By comparing the original field with the analysis field after removing the typhoon,it can be observed that the water vapor flux corresponding to the disturbance of Typhoon Swan accounts for 53.3％,which is the water vapor input of the precipitation;4) Typhoon Swan provided certain thermal conditions for the precipitation area.After the typhoon had been deducted,the large value area and warm wet tongue of the original analysis field disappeared,while the corresponding frontal area also disappeared.