A closed-loop feedback system for excimer laser pulse energy stabilization was introduced,which included a pulse energy detecting part,a switching mode power supply and a controller. Each part of the system was well shielded and the signals between the parts were transmitted by fibers. With average algorithm of pulse-pulse discharge voltage,the reliable close-loop control can be realized under the condition of strong electromagnetic interference. Tested on a 5 Hz spark discharged KrF laser,the system effectively reduced the laser pulse energy fluctuations standard deviation from 4.71% to 3.01% with a gas fill in a sound situation and from 7.18% to 3.62% with the gas in a poor situation and low discharge voltage. The method can effectively improve the stability of pulse energy.