It is the most common method to use radar reflectivity factor in quantitatively measuring rainfall amount. Based on the calculations of data of 4618 ground raindrop spectra collected from 7 observation stations over Ningxia plain during June to September in 1983, Z-I relationships in different types of rain in this region have been obtained.In addition, the effect of quantitative measuerment of precipitation with these relationships in this region is tested, and the mean relative error is about 30%.