Abstract: In order to reveal and improve the accuracy of surface rainfall rates derived from precipitation radar (PR) on TRMM satellite over the Tibetan Plateau, TRMM PR 2A25 products and hourly rain gauge data from 2005 to 2007 are compared.Results show that PR has a relative error of-35% in stratiform rain and 42% in convective rain over the Tibetan Plateau.The applicability of Z-R relation is one of the cause for the bias of PR.Based on the analysis, the initial coefficients A and b in Z-R relations at 20℃ level are modified to 0.0288 and 0.6752 for stratiform rain, respectively, also modified to 0.0406 and 0.5809 for convective rain, thus the Z-R relation at different altitudes between 0℃ and 20℃ height are updated. Results suggest that the modified models can achieve better accuracy in estimating surface rainfall rates over the Tibetan Plateau.