To understand the response patterns of water quality in the front pond of drainage pumping station to rainfall characteristics, the high-frequency online automatic monitoring was carried out for water quality and rainfall at two drainage pumping stations along the Qinhuai River in Nanjing City. The regression tree method was used to analyze the variations in the water quality (ammonia nitrogen and CODMn) of typical urban drainage pumping stations under different rainfall intensities and previous drought duration conditions, and the main influencing factors of water quality for different types of drainage pumping stations were explored. Taking ammonia nitrogen as an example, the concentration in the front pond of drainage pumping station A, which receives the domestic sewage inflow during both rainy and non-rainy days, decreases under heavy rain intensity, increases first and then decreases under moderate rain intensity, and gradually rises under light rain intensity. The water quality concentration in the front pond of drainage pumping station A is mainly affected by the rainfall intensity and secondary rainfall. The water quality concentration in the front pond of drainage pumping station B, which mainly receives the rainfall runoff but also has the inflow of domestic sewage during heavy rainfall, firstly increases and then gradually decreases under heavy rain intensity, decreases under moderate rain intensity, and has little change under light rain intensity. The water quality concentration in the front pond of drainage pumping station B is mainly affected by rainfall, previous drought duration and rainfall intensity. The response patterns of CODMn concentration to rainfall in the front pond of the two pumping stations is similar, but the concentration of CODMn is more affected by the surface runoff erosion associated with previous drought duration. Continuous rainfall causes large fluctuations in the concentration of ammonia nitrogen and CODMn in the front pond of drainage pumping stations, and longer previous drought duration results in worse water quality in the front pond of drainage pumping stations after rainfall events.