Abstract: In view of the rapid development of urban construction in Zhenjiang City, Jiangsu Province, and the release of the new version of Outdoor Drainage Design Standard (GB 50014—2021), the existing rainstorm intensity formula is difficult to meet the new requirements of urban and rural green transformation. Based on the rainfall data of Dantu Meteorological Station for 42 consecutive years from 1981 to 2022, the formula of rainstorm intensity in Zhenjiang was studied in depth. Through frequency analysis and parameter fitting, the P-III distribution is determined as the optimal fitting model, and a new 4-parameter rainstorm intensity formula is obtained. The results show that the design rainstorm intensity calculated by the new formula is about 3.7% lower than that calculated by the old formula, which is more consistent with the characteristics of actual rainstorm. The analysis of Jurong City and Nanjing City reveals the regional and temporal variation of rainstorm intensity formula. The study emphasizes the importance of regularly updating the rainstorm intensity formula to ensure the safety of urban drainage and waterlogging prevention and adapt to climate change. The research results can provide a reference for urban planning and drainage system design of Zhenjiang City to control rainwater overflow pollution.