Abstract: For the laser system performance,the threshold condition is of great significance.The threshold condition of C→A transition low gain,broadband-pulsed excimer laser is closely relative to the pump pulse.Based on the rate equations of four-level laser energy systems,the analytical methods of gain switching and Q-switch are used to study the threshold condition of the(C→A) transition low gain pulsed excimer laser.While the threshold conditions in the different gain duration are given.The analytical results show the threshold condition of the C→A transition low gain excimer laser is fundamentally different from the CW laser in short gain pulse,and depends on time integrated gain coefficient that has to exceed a critical value.