Abstract: The life-span limitation of Cesium beam tube(CBT)is the most serious shortage in our research.Along with the development of science and technology,there is many requirements to the CBT's life-span.Nowadays,the lifespan is the fatal problem in the CBT's research.In this thesis,we introduced the principle of CBT and the influence factors of CBT's life-span,especially two factors,one is Cs Oven used up metal cesium,the other is the attenuation of the electron multiplier along with the working time increasing.