In order to meet the requirements of refinement rainfall prediction in the urban rainstorm waterlogging model. Based on the urban rainstorm waterlogging model of Tianjin, the products of quantitative estimation using jointly radar and rain gauges are used in area rainfall calculation of the urban torrential rain waterlogging model. Based on four products of quantitative estimation using radar and two interpolation methods, a test of rainfall calculation in the urban torrential rain waterlogging model based on the torrential rain process in Tianjin on 25 and 26 July 2012 is performed. The comparison indicates that the variational method is the best in the quantitative estimation of precipitation using jointly radar and rain gauges in combination with a curved surface interpolation method to calculate the area rainfall.