The effect of nominal hydraulic retention time, water depth and antecedent resting period on organic matter removal performance of constructed wetland treating runoff under stochastic intermittent constant inflow was investigated through orthogonal experiments. Results indicate that effect rank of the 3 running parameters on CODCr removal rate is: hydraulic retention time (HRT)＞water depth＞antecedent resting days, and HRT has more significant effect on CODCr removal than the other two parameters. CODCr removal rate increases with the increasing of HRT, however, the effect of HRT on CODCr removal rate becomes unobvious when HRT is longer than 36h. The shorter the HRT is, the greater the effect of antecedent resting period on CODCr removal rate is. The difference in CODCr removal rate is not obvious for constructed wetland with water depth of 0.2 m and 0.4 m, however CODCr removal rate decreases significantly when water depth rises to 0.6m which might result from the decreasing ability of oxygen transfer and hydraulic efficiency in wetland bed. Average concentration of CODCr of water column in weland bed decreases with the increasing of antecedent resting days, but UV254/CODCr increases significantly, which indicates that inner system organic production increases from macrophyte roots exudation and metabolic activity of microorganism.