Using the radar echo data, a heavy rain event occurred in the northwestern Sichuan basin from 18 to 20 September of 2001 is investigated. The results show that the strong precipitation area is coincided with the echo variation with the intensity of 45dBz. In fall season, when the strong echoes with 45-55dBz presented in the floccose echo region, the radar warning observation should be conducted. Furthermore, the middle intensity echoes in the flooding region should also be tracked and observed, and the service to the users should be made.