Abstract: Quinclorac，which was a common chemical herbicide in rice field in China its characteristics and mechanism was summarized. The history of the quinclorac caused drug harms to tobacco in Chinese tobacco producing areas were reviewed，the symptoms of drug harms were described, the reasons how the harms happened and how to prevent harms were analyzed. Through most of the rest, practice, it was the conclusion that quinclorac was effective chemical herbicide, the drug harms to tobacco could prevent. Rotation and rational use could avoid the drug harms due to quinclorac. Then once the drug harms occurred, tobacco malformation caused by he drug harms couldn’t recover. The basis and technical guidance were provided for rational application and preventions of the tobacco harms occurrence.