Crystal of Cr~(4+):YAG has been widely used in LD end-pumped solid-state laser. But compares with actively Q-switched laser, its controllability is bad, influence pulse output stability seriously.The concept of pre-pumping has been presented in order to improve the stability and the controllability of passively Q-switched laser. After this,there also has the related experimental study, has proven the rationality of pre-pumping technology by the experiment. But in fact, it's very difficult to obtain ideally power source which is used in the pre-pump technology.This paper deeply discusses the factors which influence the stability of passive Q-switched laser, and discusses the relationship between power supply and the frequency stability. Based on these a programme of jumping current power supply is presented for pre-pumping passively Q-switched laser.In this plan, the pre-pump power source was divided into the control circuit part and current controlled power supply, this kind of separation formula's design proposal guarantees the current controlled power supply and control circuit's independence, is advantageous in enhances the respective stability. Not only simplify pre-pump power source's hardware architecture, but also enhance the system's performance-to-price ratio, strengthened the complete machine automaticity and expansion ability. Adjust the control electric circuit's pre-pumping control voltage and the duration, the peak voltage and the duration may change the output of current supply the pre-pumping electric current size and the duration, the summit current size and the duration. The small voltage control the big electric current has been realized.The hardware foundation for the electric current large scale jump has been provided.Ideal current output and ideal LD power output have been obtained in the experiment,which has satisfied the design requirements, establish foundation for enhanceing the frequency stability of passively Q-switched laser.