Abstract: This paper deals with the full study and analysis on the effects of MCPA on monocotyledonous turf and the control effectiveness to the lawn weeds in different dosages. The experiment results shown that: When the dosage is larger than 6000g/hm2, slight phytotoxic effect occurred. The larger dosage, the server the phytotoxic effect. When the dosage is less than 1500g/hm2, weed control effects were not evident. The economically rational dosage of MCPA is set as 3000~4500g /hm2. The lawn weeds can be effectively control at 2~4 applications annually. The application conditions and precautions of MCPA were also proposed which serves as scientific foundations for lawn weeds control.