Abstract: The nozzle,in laser welding,plays avery important role in ensuring the protection of melting pool and the qualities of laser welding.In order to get the theoretic gists for designing the structure of nozzle and adjusting the technological parameter,the jet's form of double-layer nozzle used in laser welding was systemi- cally researched in the experiment by a two-reflector schlieren instrument and analysed with the principle of aerodynamics.The results showed that,in the case without laser kindling,to obtain the satisfying length in laminar flow of shielding gas and velocity of flow,the Reynolds-number of single-layer nozzle's free-jet should range from 400 to 700.Nevertheless,for the double-layer nozzle,the Reynolds-numbers of the inner and the outer layer should be kept close to each other in order to get the best laminar flow form.Several gas outflow forms about nozzles and a protect-curtain are also shown in this paper.