The invention discloses a cleaning agent for polyacrylamide contaminated films, and a cleaning method thereof, wherein the cleaning agent comprises a pre-soaking liquid before the use of a membrane, and a cleaning liquid after the use of the membrane, the pre-soaking liquid is a soluble anionic polymer aqueous solution having a mass concentration of 0.01-10 wt%, and the cleaning liquid is an aqueous solution containing 0.01-8 wt% of sodium hydroxide and 0.01-6 wt% of a soluble anionic polymer. The cleaning method comprises: soaking a filtering membrane in a soluble anionic polymer aqueous solution having a mass concentration of 0.01-10 wt% for 3-12 h; taking out the pre-soaked filtering membrane, filtering all kinds of influents containing polyacrylamide residues, and stopping the filtering when the membrane flux is seriously attenuated and the membrane is seriously contaminated; and carrying out circulation flowing rinsing on the contaminated filtering membrane surface for 3-200 min by using a cleaning liquid. According to the present invention, with the cleaning agent and the cleaning method, the cleaning is complete, the flux of the contaminated membrane is restored, and the membrane can be reused.