Abstract: In the field of engineering, fatigue fracture of welded components is very easy to occur, which has attracted extensive attention in various industries.In order to analyze the microstructure and fatigue properties of typical welded components, T-joint were studied in this paper.Welding tests of T-joint of S355 steel were completed by MIG welding, and microstructure and hardness of welded joints were analyzed.The weld mainly contained pro-eutectoid, ferrite pearlite, granular bainite and a small amount of acicular ferrite.Composition and microstructure of fusion zone were not uniform, grain size was not consistent, and grains of overheated zone were coarser and uneven.Microstructure of normalized zone was mainly ferrite and pearlite, and grains were fine and uniform.Hardness of welded joints was higher than that of base metal, and hardness of heat-affected zone was the highest.Axial high-cycle fatigue tests on welded specimens of T-Joints were conducted, test data was processed and fitted by the least square method, and S-N curve was obtained.