Based on the observation data of New Generation Weather Radar (CINRAD) and hourly surface rain gauge data, a subsection optimized ZI relationshi p was obtained, the rainfall measurements were conducted in Xiang hongdian and Fozil ing subcatchments which located in the upper reaches of Pihe. The results show t hat by this optimized relationship, the ratio between the basin accumulated area rainfall and rain gauge value improved from 39% to 73% while the correlatio n coefficient from 0.78 to 0.8. On the 528-hour time sequence of Foziling subcatch ment with the optimized ZI relationship, the trend line slope of mean area rainfall increased from 0.40 to 0.72 compared to rainfall from rain gauge, while the ratio between the accumulated area rainfall value above 1mm/h and the accumulated rain gauge value improved from 48.4% to 85.9%. Obviously, optimized ZI radar rainfall value is closer to the observed rainfall value, and the precision of area rainfall by radar is strictly improved.