Abstract: Based on the data of OTT Parsevel² laser raindrop spectrometer, weather radar and surface rain gauge, this paper analyzes the main rainfall periods of a short-term heavy rainfall weather process in Qianjiang district on June 28, 2019.According to the common expression Z=AI^b of reflectivity factor (Z) and precipitation intensity (I), the least square method is used to fit the relationship Z-I of raindrop spectrum Z=388I^1.3, and the optimization method is used to calculate the radar Z-I The relationship Z=50I^1.1, and then the default radar Z-I relationship Z=300I^1.4 in WSR-88D are used to estimate the rainfall in the main precipitation period of Qianjiang, and the rainfall is compared with the actual rainfall. The results show that after the radar echo correction, the precipitation estimated by Z-I relation of raindrop spectrum is the best, which is close to the actual situation.It is proved that it is feasible to modify the radar echo by raindrop spectrum data to establish the local Z-I relation of all kinds of rainfall types in Qianjiang. The method can be used to estimate the precipitation intensity and regional precipitation in the future, make fine forecast, and carry out meteorology pertinently the service provides a good reference method, which is close to the actual situation; it proves that it is feasible to modify the radar echo through the raindrop spectrum data to establish the Z-I relationship of various rainfall types localized in Qianjiang, which provides a reference method for quantitative estimation of precipitation intensity and regional precipitation in the future, fine prediction and targeted meteorological services.