Abstract: Using GTAW+SMAW combined welding method to weld Q345R steel,obtain welded joints,study its microstructure and mechanical properties,the results show that the base material of Q345R steel is organized as a ribbon distribution of ferrite and pearlite,fine ferrite and pearlite distribution is uniform in welded joint area,and the microstructure in the heat affected zone is ferrite and pearlite.The tensile and impact tests of welded joints show that their mechanical properties meet the requirements.It is found that the hardness of Q345R welded joint in weld metal is the highest,followed by that of heat-affected zone,and the hardness of base metal is lowest.