The invention discloses a preparation method of high-strength high-density HTPB. The preparation method comprises the following steps: preparing materials; dehydrating an HTPB prepolymer; dispersing a surfactant and micron order SiO2; uniformly stirring the treated HTPB prepolymer and a mixed liquid, then adding a curing agent to continue to stir the mixture uniformly, and keeping the temperature at 50-55 DEG C to obtain a mixed material; performing moulding by casting on the mixed material by using a vacuum pouring device, and controlling the temperature of the material at 53-58 DEG C and the degree of vacuum being less than or equal to -0.092Mpa; and heating and curing: putting the poured mould at 50-60 DEG C and heating the mould for 12-15h, and then opening the mould. By introducing micron order SiO2 and matching with a plasticizer DOA and a surfactant Span 80, the density and strength of the HTPB can be effectively improved, and meanwhile, a better rheological property of HTPB is maintained.