To effectively evaluate and quantify the waterlogging reduction, regulation and storage capacity of sponge construction before and after the transformation of the old urban area, we studied the sponge transformation of Xiaozhai old urban area in Xi’an. Storm water management model (SWMM) was used to calculate the node overflow and the pipeline discharge under different working conditions. According to the principle of water volume conservation, the corresponding water volume of infiltration, storage, and drainage was calculated respectively. Then, indicators such as percentage of infiltration, water storage and external discharge were used to analyze the reduction effects of sponge measures on the rainfall runoff in Xiaozhai, and to evaluate the outcome of the urban reconstruction project. The results show that under the designed rainfall condition with a rainfall of 17.2 mm and a rainfall duration of 2 h, the runoff control rate of the whole area was 67.10% before sponge construction, but it reached 82.52% after that. Under other designed return periods, there was always a significant improvement after the construction. After sponge transformation, rainwater was largely stored by sponge measures, and the runoff control effect was significantly improved. In addition, the percentage of water storage increased significantly; however, the regulation and storage capacity of these measures gradually became saturated with the increase of the return period. When the return period was 100 a, the comprehensive water storage capacity of sponge measures in this area reached 353,590 m3. The research results can provide some reference for the prevention of urban waterlogging and the effectiveness evaluation of sponge facilities in old urban areas.