The invention discloses an automatic cut-off machine of thin-walled pipes, comprising a lathe bed, an operating platform, a support, an air cylinder fixing frame, a cutting frame, a guide rail frame, a V-shaped groove guide rail, a V-shaped groove frame, a locating screw rod, an air cylinder I, an air cylinder II, a V-shaped groove pressing plate, an air cylinder III a cutting frame pressing plate, a circular saw web, a driving machine, a rotating shaft, a lever, an air cylinder IV, a fulcrum, a control center, a displacement sensor I, a displacement sensor II, an oil source, a saw web slot, a cooling oil pipe, a bearing frame, a regulating head, a linear bearing, a displacement sensor III and a V-shaped groove. The control center controls the air cylinder I, the air cylinder II, the air cylinder III and the air cylinder IV respectively through the driving machine, the displacement sensor I, the displacement sensor II and the displacement III so that a plurality of thin-walled aluminium pipes transversely placed in the V-shaped groove frame are sequentially subjected to circular actions such as pressing, feeding, cutting and the like, the cutting work of the whole thin-walled aluminium pipes realizes automation, and the working efficiency is greatly increased due to simultaneously cutting a plurality of pipes.