The invention provides a U-shaped radiant tube. The U-shaped radiant tube is provided with a U-shaped flue gas duct. The U-shaped flue gas duct comprises a smoke exhaust side channel and a combustion side channel. The U-shaped radiant tube comprises a heat exchanger, a nozzle and a rotational flow device made of a non-metal material, wherein the heat exchanger is arranged at the tail end of the smoke exhaust side channel of the U-shaped radiant tube, the nozzle is arranged at the head end of the combustion side channel of the U-shaped radiant tube, and the rotational flow device made of the non-metal material is arranged in the smoke exhaust side channel of the U-shaped radiant tube and located between the heat exchanger and the nozzle. The heat exchanger comprises a pipe body and metal fins arranged in the pipe body. By the adoption of the U-shaped radiant tube, the production energy consumption can be lowered effectively, the capacity of the radiant tube can be improved effectively, and the U-shaped radiant tube is especially suitable for transformation with the requirement of lowering the energy consumption or the requirement of improving the heating capacity of the radiant tube.