The invention discloses preparation of mineral radiative powder and application thereof to a building heat-insulating coating. The mineral radiative powder is formed by mixing SiO2, Al2O3, MgO, Fe2O3, ZnO, Cr2O3, Co2O3, Ni2O3 and B2O3 proportionally, and performing three-stage calcination at 900 DEG C, 1,000 DEG C and 1,250 DEG C; the prepared products are mainly defective spinel phases, and the defective structures have a radiance of 0.94 within the wave band of 2.5-25 [mu]m. The filler provided by the invention is prepared through the three-stage calcination, and the calcinated products are of defective spinel structures; impurity ions cause lattice distortion, the symmetry of lattice vibration is reduced and the anharmonicity of polarized vibration is increased, which causes phonon combined radiation; the lattice distortion enhances radiance of infrared rays, so that the prepared coating has good radiative heat insulating performance.