The invention discloses a preparation method of 2-amino-4'-fluoro-diphenyl ketone. The preparation method comprises the following steps that ortho-nitrotoluene is chloridized by chlorine gas to obtainO-nitrotrichlorotoluene; then the O-nitrotrichlorotoluene performs Fridel-Crafts hydrolysis reaction with fluorobenzene to obtain 2-nitryl-4'-fluoro-diphenyl ketone; the 2-amino-4'-fluoro-diphenyl ketone is obtained through reduction. The synthetic route of the method is green and friend to the environment, the yield is high, the prepared 2-amino-4'-fluoro-diphenyl ketone is high in purity, the starting raw materials are cheap and easy to obtain, and the method is low in cost, easy to operate and suitable for industrial production.