Abstract: The side-axis plasma-MAG hybrid welding process with V-style 30° narrow angles was conducted to solve the problems of the MAG welding deformation and the back shaping of the root weld bead for bogie frame. In this paper, the butt plate of SMA490BW weathering steel was regarded as the research object. A mathematical relationship model was established between the plasma current, MAG current, welding speed, plasma gas flow which affect the weld penetration and the penetration, back reinforcement of root pass based on response surface method, and by means of this model, the influence of the plasma-MAG hybrid welding process parameters to the weld penetration capability was analyzed, so as to get the suitable hybrid welding process parameters. Compared with the ordinary MAG welding process, the narrow-groove plasma-MAG welding process is able to ensure the full penetration of weld root and to reduce welding deformation of the joint effectively.