Abstract: The ultra-high vacuum maintenance characteristic affects the specifications and the life of the cesium beam tube(CBT),which is one of the key technical of the cesium atomic clock.During the CBT vacuum encapsulation,specify the appropriate degassing process for different materials to reduce the outgassing rate,and rely on sputtering ion pump to keep the CBT on ultra-high vacuum environment.The operation pressure was calculated,and the technical specifications of the pump,the variation of oven temperature with pressure and the performance of vacuum maintenance of CBT were experimental evaluated.The results provide the reference for the testing and development of the magnetic state-selecting CBT.