Abstract: Small and micro-satellites are playing more and more important role in current and future space missions. Small spacecraft provide limited space and weight for thermal control system. As an important thermal control technology of spacecraft,the variable emittance devices is of great significance for reducing the load and volume of spacecraft as well as adapting to wide temperature swing in space. Thermochromic smart variable emittance devices can meet the loading requirement of small spacecraft and realize efficient thermal control. The basic principles and progress of both active and passive emittance thermal control devices are summarized. In which,the vanadium dioxide based thermochromic variable emittance thermal control device is introduced in detail. The basic principle,preparation methods and research progress are presented,and the development of variable-emittance thermal control technology is prospected.