The invention discloses a preparation method of a polyurethane integral skin seat cushion. The preparation method includes following steps: (1) uniformly mixing the following components, by weight, 60-80 parts of polyether polyol 703 and 20-40 parts of polymer polyol 3630 to prepare a polyether polyol main material; (2) uniformly mixing following components, by weight, 100 parts of the polyether polyol main material, 4-6 parts of a crosslinking agent, 0.5-1 part of a catalyst, 0.3-0.8 parts of a foam stabilizing agent, 15-25 parts of a flame retarding agent, 10-15 parts of a foaming agent and 1-2 parts of a pigment to prepare a polyether polyol composite material; and (3) mixing the polyether polyol composite material with modified isocyanate according to weight part ratio of 100:35-45, and performing foam moulding to form the polyurethane integral skin seat cushion. The polyurethane integral skin seat cushion is high in rebound rate and is effectively prolonged in service life. The invention also discloses the polyurethane integral skin seat cushion prepared through the preparation method.