The invention relates to polyurethane foam used for a low-density automobile instrument panel, a preparation method and an application thereof. The polyurethane foam comprises a first component and a second component, the first component comprise polyester polyol, the second component comprises an isocyanate performed polymer and crude isocyanate, and the isocyanate performed polymer is prepolymerized by the crude isocyanate and a straight chain polyol. The polyester polyol is used for substituting the current high-viscosity vinyl polymer grafted polyether polyols, so that the viscosity of the first component is reduced, density is reduced, and the requirement for lightweight of automobile can be satisfied. In the second component, the crude isocyanate and the straight chain polyol are used for prepolymerization to prepare the modified isocyanate performed polymer, then the isocyanate performed polymer and the polyester polyol required by polyurethane foaming in the first component are subjected to a reaction, the foams with low glass-transition temperature are prepared, so that low-temperature explosion performance of the foams is increased.