Abstract: A microcosm experiment was conducted to study the effects of  different concentration chlorimuron-ethyl (20, 200, and 2000 μg·kg^-1 soil) and its combination with urea (120 mg·kg^-1 soil) on the dynamic changes of soil microbial biomass carbon and nitrogen and soil nitrate nitrogen and ammonium nitrogen. Applying chlorimuronethyl alone decreased the soil microbial biomass carbon and nitrogen throughout the experiment period (60 days), and the decrement increased with increasing chlorimuronethyl concentration. Chlorimuronethyl had little effects on the soil ammonium nitrogen and nitrite nitrogen in the early period of the experiment, but increased the soil ammonium nitrogen in the midperiod (15 d) and the soil nitrate nitrogen in the late period (after 30 days) significantly. Both urea addition and its combination with chlorimuronethyl increased the soil microbial biomass carbon and nitrogen obviously in a short time, but the effect of combined addition of urea and chlorimuron-ethyl weakened then. Applying urea and its combination with chlorimuronethyl resulted in a lasting increase of soil nitrate nitrogen and ammonium nitrogen.