[Objective] This paper studied surrounding rainwater runoff of sunken lawn by calculating the dynamic runoff coefficient of runoff process and the runoff reduction rate.[Methods] The sunken lawn was artificial made to simulate their occupied area proportion, and the surrounding rainwater with different intensity was simulated.[Results] (1) 5 cm height designed gullies can intercept 3-year, 5-year recurred storm runoff basically when sunken lawn area ratio was 30%, and the runoff coefficients was 0.30 when it were stable; (2) When the sunken lawn area ratio was 20%, the lawn with 8 cm and 5 cm height gullies could reduce runoff rates of 3-year, 5-year recurrence storm over 40%, and the stabilized runoff coefficient was 0.90. The difference of reduction rate between the two designed gully-height lawns was not significant, and 5 cm height gullies design was more economically reasonable than the one with 8 cm gully; (3) The runoff rate from the lawn was a temporal unimodal curve. The peak flow rate was bigger and runoff duration was longer when the catchment area or the rainstorm intensity was greater.[Conclusion] Runoff reduction of sunken lawn was obvious, which was greater when the area ratio was higher.