The initial rainwater runoff pollution control rate is the key link of urban rainwater comprehensive control, and is also the key control index of Sponge City Construction Technical Guide -- Planning and Design of Rainwater System for Low-impact Development. Urban runoff has obvious initial scouring effect. But due to the randomness and complexity of rainfall scouring process, it is still a difficult problem to determine the initial runoff abandonment flow under different conditions. Taking the municipal supporting infrastructure project for the resettlement area of Anzhou Characteristic Town in Xiong'an New District as an example and taking the initial rainwater interception network of Anzhou Characteristic Town as the research object, the local study results of the volume regulating method, rainstorm intensity method and SWMM model analysis method are summarized. And the results of initial rainwater abandonment flow are compared and checked each other through these three calculation methods. Finally, the initial rainwater abandonment flow of this area is determined. Hereby, the relationship among the initial rainwater abandonment flow, runoff pollutant concentration change and runoff pollutant removal rate are further studied, which provide some reference for practical engineering application.