Rare-earth tungsten thermionic emission material was used in the high-temperature electrostatic dust removal technology. A static test facility was self-designed to explore the emission characteristic. XRD, SEM and EDS were used to analyze the microstructure and element distribution. Working in high-temperature and oxidizing condition, tungsten in the thermionic emission materials is oxidized to tungsten trioxide, but the rare-earth tungstate in the grain boundary has no chemical changes. In high-temperature and oxidizing ambience, there is oxidation and volatilization on the surface of rare-earth tungsten, resulting in materials loss. The degree of loss depends on the composition of gas.