Based on WSR-88D radar data, the radar echo′s characteristics of the torrential rain in Shanghai on the night of August 5th 2001 are analyzed to find out its precipitation mechanism and characteristic.It is found that a south wind velocity convergence on the side of subtropical high,the echo′s consolidation in the spiral rain band,convergence caused by wind′s perpendicular shear and high precipitation rate of tropical system are the precipitation mechanism and characteristic of the rain event.Some key points are presented about forecasting this kind of heavy rain events:heavy precipitation echo′s appearance and development are always related with local strong convergence in wind field,local convergence′s appearance and evolution can be found from the continuous change of Doppler radar wind data,thus,the forecast of heavy precipitation′s probability can be made.