Based on routine weather data, meteorological elements fields, wind profiler radar data, satellite cloud images and operational numerical forecast data， we have analyzed a heavy rain event that occurred in Shanghai in 23-24 August 2015. The results show that it was caused by combined action of a remote tropical cyclone Goni and cool air spreading southwards from north area; the circulation of Goni provided the plentiful supply of water vapor and energy required for the event; and the convergence of cool wind and strong easterly jet enhanced vertical motion of moisture air. Verification indicates that there are remarkable bias in rain hit areas, intensity and timing for most operational numerical forecast, which possibly come from the errors in calculation of TC position, strength and location of easterly jet around TC and strength of cool air, etc. Under such situation we should devote much attention to the application of real time observation with the aim of issuing available short term early warning of heavy rain.