Aiming at the hole defects in the welded joints, by the ZL-2 super pulse discharge generator, the welded joints of 9CrSi steel with hole defects were discharged by electromagnetic heating and the fatigue life were tested before and after discharge by using self-designed fatigue testing machine. The discharging instant stress intensity factors were theoretically calculated. The result shows that there is an optimal discharge voltage for the fatigue life. Under the action of 5.5 kv pulse discharge voltage, the average fatigue life of welded joints after discharge are increased by 10%. The electrothermal stress intensity factor is negative that weaken the crack driving force, thereby extending the fatigue life of the welded joints.