A long-pulse TE CO2 laser with ultraviolet-preionization using pulser/sustainer discharge technique is presented. The laser can discharge stably with 14 nF pulser capacitance and 200 nF sustainer capacitance by optimizing the parameters of pulse forming network and amending the Chang’s profile. For an active volume of 2.48 L, a gas mixture ratio of CO2, N2, He is 1∶2.5∶13 and the gas pressure of 40 kPa, the maximum output laser energy of 18.51 J with a pulse width of 32 μs is obtained at an efficiency of 14.3%.