The invention provides a pipeline inner wall laser cleaning device based on side wall projection. The pipeline inner wall laser cleaning device comprises a motion control unit and a laser transmission scanning unit. The motion control unit comprises a movable main unit platform, an automatic rotating shaft, a horizontal moving platform, a height adjusting unit, an electric horizontal supporting rod, a first servo motor, a first ball screw and a rotatable laser range finder. The laser transmission scanning unit comprises an optical fiber laser, a transmission optical fiber, a laser head, a support, a concave lens, a convex lens, a second servo motor, a second ball screw, a screw slider, a lens bracket, a reflector, a reflector bracket, a scanning galvanometer and a field lens. After being emitted, a laser beam propagating in the axial direction of a pipeline passes through the concave lens, the convex lens and the reflector and then enters the scanning galvanometer, and through the scanning galvanometer, the laser passes through the field lens and then is focused on dirt on the inner wall of the pipeline. According to the pipeline inner wall laser cleaning device, a machining head or the pipeline does not need to spin in the whole machining process, and the bottleneck problem that a traditional laser cleaning technology is difficult to apply to cleaning of the inner surface of the pipeline is solved.