Inflow pattern is one of the main factors that affect the hydrological regulation performances of grassed swales for urban stormwater runoff control. The artificial simulation test device of grassed swales is manufactured to discuss the effect on runoff and peak flow under different inflow patterns. The results show that the source centralized inflow, peripheral multipoint inflow and peripheral overland inflow of grassed swales under 4-m3/h inflow load can reach 7.06%, 8.33% , 9.51% for total runoff control rate, and 2.67%, 5.83% , 6.44% for peak flow reduction rate. Meanwhile, the delay time of peak runoff is 9.6 min, 10.3 min and 12.2 min respectively compared with traditional pipeline. The above shows that the peripheral overland inflow is better than other inflow patterns of grassed swales on rainwater hydrological regulation performances.