【Objective】To study the effects of pendimethalin on soil enzyme activities in cotton field.【Method】Pendimethalin at different concentrations (0，2 700, 4 050, 5 400 g·hm^-2) were applied to cotton field. Changes in soil enzyme activities at different soil depth and treatment time were investigated.【Result】After treating with pendimethalin,alkaline phosphatase activity was substantially inhibited, and was inhibited the most at the soil depth of 5-10 cm 40 days after treatment.The inhibition rates of 2 700, 4 050 and 5 400 g·hm^-2 treatments were 93.79%, 90.77% and 87.43% respectively. Urease activity had been continuously activated. Sucrase and dehydrogenase activities increased with the concentration of pendimethalin increasing, and the enhancements of the soil surface were significantly stronger than those at the soil depth of 10-20 cm. Catalase at the soil depth of 0-10 cm was firstly inhibited and then activated with the treatment time increasing.【Conclusion】Pendimethalin can activate urease and catalase, inhibit alkaline phosphatase, and reduce the soil available phosphorus content in cotton field. Longterm application of pendimethalin can cause soil nutrient imbalance.