The invention discloses a preparation method of a filter rod material acetate fiber lowering cigarette harm. Additive is added in prepared spinning size in the production process of the cigarette filter rod material acetate fiber, wherein, the adding amount is 1-15% of the weight of the size; the additive is one or more of sodium bicarbonate, potassium bicarbonate and sodium carbonate. The preparation method of the invention reduces harmful substances in main stream smoke, and simultaneously improves filtering effect of cigarette filters, thus improving abstract qualities of cigarettes and protecting the health of smokers. The preparation method of the invention has simple process, and provides a scheme for large scale production of the filter rods which reduce harmful substances in main stream smoke.