In metal laser cutting machine actual cutting process, it has a limited cutting thickness. Combustion process can be continued, temperature of cutting edge must reach ignition. Alone by the combustion energy released by the reaction, in fact it can not ensure combustion process continues. On the one hand, due to be slit nozzle oxygen stream continuous cooling, reducing the forefront of cutting temperature: On the other hand, combustion of ferrous oxide layer is formed to cover the surface of the work piece, impede the diffusion of oxygen when the oxygen concentration is reduced to a certain extent, the combustion process will be extinguished. Traditional convergent laser beam cutting, the laser beam is applied to a small area of the surface, due to the high power density of the laser, so that not only in the area of the laser radiation, the surface temperature reaches the ignition point, and as heat conduction, a wider region has reached ignition temperature. The diameter of oxygen flow to the work piece surface is larger than the diameter of the laser beam. This indicates that not only in the region of the laser radiation, combustion reaction to occur strongly, and the periphery of the spot of the laser beam should occur simultaneously burning. When the slab cutting, the cutting speed is quite slow, surface iron oxy-fuel cutting head speed faster than traveling. After a period of time of combustion, since the oxygen concentration decreases, which leads to burning off process. Only when the cutting head travels to this position, the combustion reaction begins again. Cut the forefront of the combustion process is carried out periodically, which would result in the forefront of cutting temperature fluctuations, cut quality deteriorates.