Abstract: This paper analyses the reasons of the shock producing when the conventional nozzle is working at the high pressure in laser cutting, and the harmful effects of the shock in laser cutting. In order to solve this problem, a new method for the design of a supersonic nozzle is presented. This supersonic nozzle consists of four sections:stable,convergent,throat and divergent. Each of these sections is designed strictly based on gas dynamic theories. The exit jet from this type of nozzle with high momentum, good uniform and a tidy boundary can be obtained. Laser cutting speed and quality can be efficiently improved by using this type of nozzle.