The invention discloses modified polyurethane. The modified polyurethane is formed by mixing and foaming a white material and a black material. The white material is premixed polyether, and the black material is isocyanate. A promoter needs to be added in the foaming process, and comprises a catalyst, a foaming agent, a cross-linking agent and a foam stabilizer. The mass ratio of the black material to the white material is larger than 1.8:1. No fire retardant is added in the preparation process of the modified polyurethane. The prepared modified polyurethane is of a hexatomic ring molecular structure. The prepared modified polyurethane contains no halogenate fire retardant, has more excellent fire retarding performance, and is low in cost, free of toxins and environmentally friendly, and the fire retarding performance is not lowered as time goes by. It is determined through tests that the oxygen index of the modified polyurethane is not smaller than 32, the density degree of smoke is smaller than 75, and the heat conductivity coefficient is not larger than 0.024 W/m.K.