The distribution and nonuniformity of the electric field have been simulated in the active medium of CO₂ laser using successive-over-relaxation numeric method. The different configurations of UV preionization have been considered as spark array, surface corona, plasma cathode, and sliding discharge. The electric field distribution and field deviation (FD) is compared in various configurations to obtain an insight into the electrical field uniformity. The numerical simulation results show that the minimum FD is related to the plasma cathode and sliding discharge configurations regarding boundary conditions. For the sliding configuration, a slight increase in the FD was observed in comparison with plasma cathode. The FD of surface corona configuration is about two percent lower than the spark array.