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　systemically　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.