Abstract: This paper firstly derives expressions of current and voltage at various work modes for the series resonant charging power supply, gives recursion formulas calculating the value of current and voltage at various periods; secondly, utilizing recursion formulas, it makes out that the power supply characterizes pulse constant current charging; thirdly, this paper calculates the parameters of the power supply when capacitor-load incompletely discharge, the power supply provides half the maximum output when capacitor-load completely discharge, and provides maximum output to maintain the voltage of capacitor-load; at last, describes a 100Hz steady operation power supply for accelerator utilizing Tesla transformer, measured results and calculated results are well consistent．