The related equations and characteristic equation were established on the basis of Changsha Doppler radar echo and surface rainfall parameter. S u rface rainfall data of 27 summer cumulus were calculated to test the established relationships, then some estimation equations about single factor or multiple fa ctors were gained. The results show that the most rain intensity is correlated w e ll with echo height in the range of 50～100 kilometers, in multiple factors corr elated equations, the surface rainfall is proportional to the horizontal scale and echo height, and is inversely proportional to the echo moving speed.