In a high power CO ₂ laser, laser gas is electrically excited by glow discharge and the quantum energy is utilized as laser beam. The gas in the discharge area is cooled by convection. However, the glow discharge phenomena are strongly related to the laser gas flow characteristics within the discharge section. Consequently, the power of CO ₂ laser device is influenced by the gas flow pattern. In order to understand the flow characteristics within the discharge section, a scale model adopting water flow is used here. A beam scan type laser light sheet and fine Al powder are adopted as the light source and particle tracer respectively. The results are as follows. (1) It is possible to take photograph which clarify the velocity of the particle with a beam scan type LLS. (2) It is possible to visualize the flow pattern within the discharge section in case without discharge.