A full butt joint structure of a connection joint between a side frame and a cross beam of a bogie frame, characterized in: the side frame is connected to the cross beam by a connecting seat to realize the full butt joint, a side frame connecting end of the connecting seat, a transport column and a side frame inside vertical plate form a plate-plate butt joint structure, and a cross beam connecting end of the connecting seat and the cross beam form a tube-tube butt joint structure. An assembly welding process comprises: the connecting seat is assembled and welded to the cross beam; a cross beam unit is assembled and welded; the connecting seat is assembled and welded to the transport column and the side frame inside vertical plate; a side frame strengthen partition plate is assembled and welded to an upper plate; and the bogie frame is welded.