The 〖WTBX〗Z/I〖WTBZ〗 relationship is derived to improve the radar rainfall estimation based on the data during the period of 2015 to 2016 observed by the Parsivel raindrop spectrometer in Longyan. The relationship is applied to estimate 6 rainfall cases from 2015 to 2018 By comparing with observed data from the automatic meteorological observation stations, we can see that the accuracy of radar surface rainfall estimation increased by 50% due to the corrected Z/I relationship.