Abstract: According to T Joint of large tilt angle laser penetration welding of carbon steel plate with 2.5 mm and 3 mm in thickness and filler wire of ER50-G, the shape and properties of T joint were systematically studied. It was investigated that the effects of welding parameters such as welding speed, wire feeding speed, laser power, the location of laser on the plate and the defocusing distance on weld formation. The microstructures and hardness of T joint were analyzed and tested. The results show that the optimized welding parameters were acquired, the welded joints welded with the optimized welding parameters are free of defects and meet the requirements. The studies will support the application of the laser welding with filler wire on the body structure of high speed train.