Abstract: In order to restrict the power dissipation and electromagnetic interference when the flash-lamp-pumped system of solid laser is at the time of burst and preignition, the technology of quasi-resonant triggering and preignition was developed.Based on this technology,a long-pulsed medical Nd:YAG laser was designed to meet the electromagnetic compatibility requirements of national medical electrical equipment.Because parasitic parameters of the pulse transformer can not be eliminated, complicated oscillation should occur in the circuit.Making use of this resonance characteristic of the pulse transformer, the triggering frequency was adjusted the same as the resonant frequency,namely,quasi-resonant state,to ignite flash-lamp.The experiments proved this circuit was reliable and stable.The value of triggering-pulsed peak voltage could descend below 10kV,much lower than the nominal triggering voltage, 16kV.The results show that the circuit completely meets the national electromagnetic compatibility standards on medical electrical equipment.