Abstract: The principles and characteristics for lasox laser cutting of thick plates are presented in this paper.The steady-state conditions for the cutting were analyzed.The finite element method was used to simulate the surface temperature field along the centerline position in the cutting process.Based on this result,cutting quality was evaluated by the function of beam diameter,cutting speed and incident power.The range of cutting speed was also predicted for 20mm thick plates.A cutting experiment was made and the results shown that 12mm and 20mm thick plates could be cut successfully by the method ,at the same time,a reasonable agreement between the numerical simulation and the experimental results was found.