The invention discloses a plain city primary rainwater regulating storage tank design method based on pollutant characteristics. The time corresponding to the maximum pollutant accumulative rates in the pollutant accumulating processes of water catchment areas corresponding to plain city regulating storage tanks serves as the rainwater runoff interception time points of the regulating storage tanks, and the volumes of the regulating storage tanks are designed by combining the runoff volume accumulating processes produced in the water catchment areas corresponding to the regulating storage tanks. By adopting the primary rainwater regulating storage tanks designed by the invention, the rationality of the design method for the primary rainwater regulating storage tanks can be provided easily,the volumes of the regulating storage tanks can be designed by scientifically utilizing pollutant accumulating characteristics, the sewage interception rate is high, the economical efficiency is alsoimproved to a certain extent, and unnecessary wasting of manpower, materials and financial resources is avoided.