Abstract: Multi-layer and multi-pass welding of Q345B steel by MAG welding and SAW process was performed,and welding thermal cycles was collected by contact thermocouple of type K,and welding induced angular distortion was measured by laser displacement sensing system during the whole welding and cooling process.The results indicate that the peak temperature of each welding cycle is increased as the weld pass is closer to measurement location,and the closer the distance between measurement location and weld,the higher the peak temperature,and correspondingly,the faster the heating rate.The angular distortion induced by welding is mainly caused during welding stage,which is gradually increased,but the distortion is very small during inter-layer cooling stage.Finally the welding induced angular distortion is about 4.78°.