This study offered a scale design method for the bioretention facilities based on single storm analysis and long seriesrainfall statistics. As for that the design return period of rainfall is usually used in municipal drainage design in China, in thescale design method for the bioretention facilities based on single storm analysis, the design rainfall process was calculated by us -ing the storm intensity formula and rainfall distribution, the facility inflow process was calculated with the design rainfall process,and the outflow process was derived by using the water balance method. In this case, the hydrological effect was evaluated by therunoff reduction rate, peak flow reduction rate and peak flow delay time. Otherwise, the long-term daily rainfall was analyzed byusing the scale design method based on long series rainfall statistics, by which the inflow and treated outflow of the facilities underdifferent rainfall frequencies were calculated and the annual runoff reduction rate was used to evaluate the hydrological effect.