The invention relates to a method for carrying out solid-phase grafting modification on polypropylene by assistance of supercritical carbon dioxide. The method comprises the following steps of: swelling the polypropylene for 0.5-10 hours in the supercritical carbon dioxide dissolved with vinyl monomer and an initiating agent, and then slowly releasing pressure; transferring the swelled polypropylene into a reaction kettle, adding interfacial dimethylbenzene according to the mass ratio with the polypropylene of being 1%, rising the temperature to 65-165 DEG C under normal pressure, and reacting for 1-10 hours to obtain a target product, wherein the swelling and penetrating temperature in the swelling process is 31-60 DEG C, and the swelling pressure is 7.5-12MPa; the initiating agent is an azo compound or peroxide, and the mass of the initiating agent is 0.1-5.0% of the mass of the polypropylene; and the mass of the vinyl monomer is 0.2-20% of the mass of the polypropylene. According to the method, the grafting rate reached 5.40%, and the grafting efficiency is over 90%. According to the method, the thermal property, the polarity and the mechanical property and the like are obviously improved and the hydrophilcity is obviously improved.