The invention relates to a light high-strength cement-based roof thermal insulation material and a preparation method thereof. The light high-strength cement-based roof thermal insulation material comprises the following components of portland cement, silica fume, hollow SiO2 microspheres, aerogel and a water reducing agent, and the preparation method of the light high-strength cement-based roof thermal insulation material comprises the following steps of taking the Portland cement in parts by weight, adding the silica fume, the hollow SiO2 microspheres and the water reducing agent, pre-stirring to form a dry mixture, adding the water into the dry mixture, stirring to form slurry, adding the aerogel into the slurry, and stirring for molding. Compared with the prior art, according to the invention, the hollow vitrified microbeads and the aerogel are bonded, the advantages of light weight, fire resistance and corrosion resistance of the hollow glass beads and the aerogel are fully utilized, and the aerogel is used for pore forming, so that the density is reduced, and meanwhile, the better mechanical property is maintained, and the light high-strength cement-based roof thermal insulation material also can keep the better mechanical property and the excellent thermal insulation property on the premise of keeping the lower density.