In order to alleviate the influence of initial rainwater on river water quality, the function adjustment is carried out of sewage plant which has been reformed as initial rainwater storage facility. Combined with the actual situation of the sewage plant, the present situation of exploitation scheme is adopted considering the factors such as investment, construction period and influence. The current structures are transformed into the initial rainwater storage tank, and the corresponding supporting facilities are added to meet the function. The application has high social and economic benefits and provides reference for other projects.