High power transverse flow CO2 laser was used to scan the brazing alloy and diamond grits. The influence of laser technological parameters on brazing layer combination performance and diamond grits thermal damage was researched, and the thermal damage mechanism of laser brazed diamond and the combination mechanism of brazing layer and diamond grits were analyzed. The research results showed that laser power and scanning speed were the main factors for diamond thermal damage and surface wetting. On the conditions of 0.5 mm brazing layer thickness, argon shield, 800 W laser power, and 8.39 mm/s scanning speed, the best combination performance among the diamond grits, brazing alloy and metallic base can be achieved. Brazing alloy wetted the diamond grits well and reacted with them to form TiC and SiC. Under high laser energy input, oxidation take placed between diamond grits and oxygen outside, diamond would be oxidized all along on the condition of branch gas pressure about free equation until the balance established between diamond and oxide, during this process, diamond grits would be carbonized or burn out and gasified.