Progress in the study of the tungsten thermionic cathode emission mechanism is summarized.The thermionic theories,such as,the monoatomic layer and dipole theory,the semi-conductor model and the model of dynamical surface emission centers,are reviewed in this paper,then the defects of them are pointed out.New progresses in study of the Tungsten thermionic cathode were introduced,especially the nanometer particles(film) emitting theory on Lanthanum Tungsten cathode and the emission theory on Scandate Tungsten...