The variable emissivity coatings or devices, based on thermochromism and electrochromism, have great application prospects to spacecraft thermal control, because of their lightness, low energy consumption and facility. The variable emissivity materials are the key of these coatings and devices, and mainly have two kinds: electrochromic materials and thermochromic materials. The application principles of variable emissivity materials on spacecraft thermal control were analyzed. The research progress of four kinds of representative variable emissivity materials, which are perovskite oxides (A_1-xB_xMO₃), vanadium dioxide (VO₂), tungsten trioxides(WO₃) and conducting polymers (CPs) respectively, are preferentially presented. Based on the total needs of spacecraft thermal control, the development trend of variable emissivity materials is discussed finally．