The invention relates to a method for reducing harms and tars of cigarettes. The cigarettes are put into air containing ozone to be treated for a section of time, wherein the ozone concentration in the air is 0.01-100 mg/m<3>, and the treatment time is 0.5-72 hours. By using the method to treat the cigarettes, the hazardous index of the cigarette mainstream smoke can be effectively reduced. The method provided by the invention has the advantages of simplicity and convenience for operation, no pollution, safety, reliability, strong applicability and the like.