The invention discloses an automatic welding device and method for pipeline butt-joint machining. The automatic welding device comprises a workbench, fixing seats, clamping frame bodies, side cover plates and clamping adjusting mechanisms, wherein the fixing seats are connected to the left side and the right side of the upper end face of the workbench; the clamping frame body is fixedly connected to the position of the upper side of the fixing seat; the side cover plates are connected to the left side and the right side of the clamping frame body; and the clamping adjusting mechanism is arranged in the clamping frame body. According to the automatic welding device for pipeline butt-joint machining, steel pipes can be conveniently, rapidly and stably clamped and fixed, so that the butt-joint precision and stability of the steel pipes can be effectively guaranteed, the welding quality of the steel pipes is improved, the steel pipes can be conveniently, automatically and uniformly welded, the welding machining efficiency of the steel pipes is improved, the steel pipes with different diameters can be conveniently welded through adjustment of a distance adjusting mechanism, and the applicability of the welding device is improved.