A 2.0 kW six-axis robot fiber laser cutting system is used to study the impact of cutting process parameters on the kerf width, bevel angle, cutting surface roughness and incision microscopic state of 6 mm thick steel plate. The results show that the optimum cutting process parameters are cutting speed about 2.0 m/min, auxiliary gas pressure 14.7 N/cm2, focusing lens focal length f=200 mm, laser spot diameter 0.3 mm, defocusing amount +4~+5 mm, cutting nozzles diameter 0.8 mm. Under the optimum cutting process parameters, the kerf width is 0.5~0.6 mm, the cutting tilt angle is 0.2°~0.5° and the cutting surface roughness is small. Cutting surface is divided into two different parts because of the top and bottom sections show different flatness. The temperature in the bottom is higher, the gap between oxidation rate and cutting rate is greater than that on the top, so the flatness is poor. Compared with CO2 laser cutting, fiber laser cutting surface roughness is better and the cutting power efficiency is increased by 2.6 times.