Abstract: The effect of rain gauge density on estimating of areal rainfall using a radar-gauge calibration algorithm is studied，which is based upon the dense rain gauge reported data and Hefei CINRAD/SA radar observed reflectivity data over the Foziling and Xianghongdian subcatchments located in the Huaihe River basin with five meiyu front precipitation events occurred during 22 June to 11 July in 2003. The Z-I relationships of Z=200I1.6and Z=300 I1.4 were both used to obtain the guessed radar rainfall, and the areal rainfall derived from 12 rain gauges were chosen as the “true” value. By reducing the number of calibration gauges from 12 to 1 gradually, the corresponding areal rainfall series based on the radargauge calibration algorithm and the rain gauge networks were obtained and compared with the “true” values. The results show that the accumulated rainfall derived without calibration has significant underestimates by about 20%-50% over both the subcatchments for all the five cases studied. The more rain gauges used, the better results were obtained, and the single gauge calibrated radar rainfall seems unstable. The results obtained using the radargauge calibration algorithm show great priority to those derived from rain gauge networks only while the gauge number and locations were fixed. Moreover, when the error of precipitation estimation is less than 10% with the stable RMSE（ERMS） and high correlation coefficients, the corresponding gauge density is one per 700 km 2 or so for the Xianghongdian sub-catchment, and per 900 km 2 or so for the Foziling sub-catchment, respectively.