In the experiment, laser cutting was performed on stainless steel and carbon steel by using high brightness diode laser as light source. The experiment verified the feasibility of the diode laser cutting, and analyzed the cutting process comprehensively. When using oxygen as auxiliary gas, most cutting energy was from the oxidation, which was promoted by laser. When using nitrogen as auxiliary gas, the main factors that influenced the cutting results included the total output energy and the laser power density. 500 W laser output power was suitable for sheet metal around 3 mm, and speed of diode laser cutting was found similar to the fiber laser in addition to the similar cutting surface and slit shape. The cutting ability of diode laser can be further improved with an optimization scheme of oxygen aided cutting technology for carbon steel, which can success in cutting 6mm thickness carbon steel.