In pulse power field, high voltage pulse capacitor is used widely, and the capacitor charger is its important primary power supply. At present, the capacitor charger usually uses high frequency switching power supply technology. But increasing charging power will lead the volume of charging power supply system to grow larger. And it is difficult to meet the miniaturization requirement. In view of this situation, this paper study the fast charger technology based on the lithium ion battery which is as a primary power supply also. The topological circuit of fast charger and the control method is discussed. At the same time, the simulation of the prototype is done in this article.