Based on the concept of natural storage, natural infiltration, natural purification for rainwater advocated the sponge city, infiltration and seepage-proof rainwater gardens were designed and built according to the rainfall characteristics in Xi'an. We monitored the runoff regulating effects in 33 rainfall events from 2015 to 2017. The results showed that:(1) Seepage-proof rain garden filled with undisturbed soil reduced runoff volumes by 11.2%~100% (medium=69.14%). (2) The results of pollutant concentration exceedance probability analysis showed that the probabilities of concentrations of total nitrogen, ammonia nitrogen, total phosphorus and chemical oxygen demand exceed the limit standard IV of the surface water quality decreased by 58.57%, 2.71%, 20.57% and 29.71%, respectively, in the rainwater flows through the garden system, compared with the exceedance probabilities of inflow concentration. (3) The correlation coefficient between the runoff reduction rate and the pollutant load reduction rate was more than 0.857 for 33 rainfall events. (4) Through monitoring the precipitation, water qualities of inflow and outflow, we estimated that the annual pollutant concentration removal was 11.93%~60.97%, and the annual load of pollutants reduced more than 70% in the rainwater garden.