The invention discloses polar polypropylene prepared through grafting modification, with supercritical propylene as a swelling agent. A preparation method for the polar polypropylene comprises the following steps: adding polypropylene, an initiator and grafting monomers into a reaction vessel; introducing propylene; carrying out heating and pressurization until propylene is in a supercritical state; and carrying out a reaction so as to obtain a polar polypropylene product. The polar polypropylene product prepared by using the method has a high grafting rate, and when the polar polypropylene product is used as a compatilizer, the addition amount of the product is small.