A heat insulating ultra-low-temperature tube comprises a tube body. A K-FLEX ST flexible closed-pore elastic foam wraps outside the tube body. An aluminum film wraps outside the K-FLEX ST flexible closed-pore elastic foam. Another layer of K-FLEX ST flexible closed-pore elastic foam wraps outside the aluminum film. Metal rings are used to fix the second K-FLEX ST flexible closed-pore elastic foam wrapping layer. An iron sheet or rubber material wraps outside the whole wrapping layer. The heat insulating ultra-low-temperature tube having the same operation principle with the prior art has the advantages that heat from the surrounded environments can be reduced from transmitting into LN G low-temperature equipment and a pipeline, LN G cooling amount loss is controlled, the outer surface temperature of the heat-insulating layer is kept higher than the dewing temperature of the environments, and condensation of the outer surface is avoided, energy is saved, and normal operation of LN G is guaranteed.