The aim of the present work is to design, construct, and simulate an axial slow flow CW CO² laser system of 150 W as output power. The simulation is based on the theoretical equations and the software programs were written in C language. Results of these programs were used in designing the system. These programs depend on assuming from parameter, which have been inferred studying similar CO² lasers to obtain the better values used in the system operation. These programs calculate output power, water-cooling temperature, spot size of the laser beam on the plane and spherical mirror, gas temperature, V-I characteristic, and line broadening mechanisms. The laser resonator consisted of two electrical discharge Pyrex tube of length 1180 mm, inner diameter of 16 mm and thickness of 2 mm for each tube. A glass jacket for flowing cooling-water surrounded the discharge tube. The back mirror of the optical resonator was a gold-coated copper mirror of 5 m radius of curvature and 25 mm in diameter, while the plane mirror used was a ZnSe mirror with reflectivity of (70, 60 %). Two negative electrical discharge electrodes (cathodes) were made of aluminum and one positive electrical discharge electrode (anode) was made of stainless steel in Teflon mounting. The vacuum system consisted of a vacuum pump, vacuum and pressure gauge, and a gas mixture. Mixtures of CO²: N²: He as well as a premixed mixture (1:2:8) was used as an active laser medium. In this project is used high voltage DC power supply with a maximum voltage of 30 kV and 100 mA.