The invention provides a method and system for measuring emissivity of a high-temperature material, wherein the system comprises a large-power radiation source, a beam expanding, reshaping and homogenizing device, a vacuum chamber, a sample test platform, a rotating planar reflector, a micro-imaging device, a light spectrum switching device, a radiation energy imaging measuring device, and a temperature measuring device. According to the method and the system provided by the invention, a blackbody cavity is machined out on a tested sample; an imaging method is used to simultaneously measure a radiation energy of a tested material surface and the blackbody cavity; a narrow band filter is employed for performing light spectrum selection, so that not only can a tested material and a standard reference sample be simultaneously measured, but also the sample and a reference source can be guaranteed to be completely isothermal, and therefore, an error resource of emissivity measurement can be remarkably reduced, measurement accuracy and test convenience can be improved, and engineering application is facilitated.