Welding　trials　of　autogenous　laser　welding,　laser　welding　with　filling　wire　and　laser-MIG　arc　hybrid　welding　were　carried　out.　The　characteristics,　causes　and　controlling　methods　of　joint　defects　were　analysed　by　optic　microscope,　X-ray　detection　and　numerical　simulation.　The　results　indicated　that　the　common　defects　were　imperfect　shape　and　porosity　inside　the　weld.　The　characters　of　weld　surface　defects　varied　during　different　welding　processes,　porosity　were　also　different　in　shape　and　formation　during　full　penetration　welding　and　incomplete　penetration　welding.　All　most　defects　mentioned　above　could　be　controlled　and　avoided　by　optimizing　the　welding　process　procedures.