Abstract: Effects of different contents of acetochlor on soil urease and its kinetic characteristics in brown soil were study in incubation days with indoor experiments. The results show that soil urease activities are obviously inhibited by different contents of acetochlor, and the peak inhibition ratios are from the third incubation day to the sixth incubation day. Two models, y=c/(1+bx) and y=c(1+ax)/(1+bx), were used to describe the effect type of acetochlor on soil urease, the fitted results show that the model, y=c/(1+bx) is more suitable, and this means the inhibition is a completely inhibition. The ED50 values calculated from the model are from 13.12 to 75.76 mg/kg. The soil urease Km is not obviously effected by acetochlor, and the V max becomes small. This kind of the effect belongs to the non-competitiveness inhibition.