The invention relates to a cylindrical heat exchanger, comprising a combustion cavity, a spiral screw sheel, an upper end cover and a lower end cover, wherein the combustion cavity is a cylinder with an opening at each of two ends thereof, strip fins are evenly distributed at the inner peripheral wall of the combustion cavity, the strip fins are parallel to the axial direction of the cylindrical combustion cavity, the two ends of the strip fins are extended to the openings of the two ends of the combustion cavity; the spiral screw sheel is sheathed on the combustion cavity, convex spiral lines are arranged on the inner peripheral wall of the spiral screw sheel, the inner edges of the convex spiral lines are in close integration with the outer wall surface of the combustion cavity, a spiral channel is formed between the outer wall of the combustion cavity and the inner wall of the spiral screw sheel; the upper end cover and the lower end cover are of cup shape respectively with an opening at the end face, respectively cover the two ends of the combustion cavity and the screw sheel and are fixed with the two ends of the combustion cavity and the spiral screw sheel by tight coupling;and the upper end cover is provided with a water inlet which is communicated with one end of the spiral channel, and the lower end cover is provided with a water outlet which is communicated with theother end of the spiral channel.The cylindrical heat exchanger of the invention features delicate and reasonable structure, convenient maintenance and cleaning, long service life, high thermal efficiency, energy conservation and durability.