Abstract: Cathode Evaporation is an important index to evaluate the capability of cathodes. It relates to the stability and lifetime of cathodes. In this paper, time of flight mass spectroscopy is used to analyze the evaporation of cathodes in different states. The results show that the new cathode is clean. It can be decomposed and activated by the normal technics. After being decomposed, there is Ba in the surface of the cathode. The lifetime and stability would not be affected by the cathode evaporation.