Abstract: In order to study electron emission phenomenon of cathode evaporator, a new designed test device is used to collect the electron emission curve of evaporator deposited on polycrystalline tungsten surface, Electron emission microscope and SEM are used to analyze electron emission image, surface appearance and composition. The results show that the emission curve can be divided into three stages, namely sharp-rise stage, fast-rise stage and slow-rise stage, which correspond to electron emission of grain boundaries and scratches, grain surfaces and three-dimensional islands sequentially. It is proved that electron emission performance of M-type cathodes can be greatly improved by building uniformly dispersed island-shape crystal emission spots.