The invention discloses a pipeline welding seam milling robot. The pipeline welding seam milling robot comprises a frame, and travelling devices which are arranged on the frame in a central symmetry mode and used for circumferentially supporting the inner wall of the pipeline and driving the frame to axially travel, a power assembly which is arranged on the frame, a milling assembly which is arranged on the frame, and a clutch assembly which is arranged on the frame and is used for distributing the power output direction of the power assembly; the power assembly can independently drive the travelling devices to stretch and contract through the clutch assembly so as to change the radius of the outer circle formed by the travelling devices, and further can independently drive the milling assembly to rotate so as to enable the milling assembly to be converted the orientation along the pipeline circumferential direction. The milling robot can move in the axial direction of the inner wall of the pipeline, the milling assembly can convert the orientation along the pipeline circumferential direction at the same time, so that the milling operation on the weld joints in all directions inside the pipeline can be realized, the milling efficiency is high, the milling quality is good, the operation is convenient, and the labor cost is saved.