Compared with traditional cables, superconducting cables have the advantages of no resistance loss, large transmission capacity and high reliability. However, polypropylene laminated paper as its main insulation has high loss factor, which leads to large dielectric loss in the operation of superconducting cables and increases the load of cooling system. In this paper, polytetrafluoroethylene filter paper with low loss factor is used to replace the kraft paper layer in the polypropylene lamination paper, and a sandwich structure composite insulation with porous surface can be formed by being hot-pressed with the polypropylene film. The test results show that replacing the polypropylene lamination paper with polytetrafluoroethylene/polypropylene composite material as the main insulation in the superconducting cable will reduce by more than half the dielectric loss. At the same time, due to the smaller dielectric constant difference between the polytetrafluoroethylene/polypropylene composite material and the liquid nitrogen used as the coolant in the high temperature superconducting cable and the volume effect of liquid nitrogen breakdown, the low dielectric loss composite insulation made of polytetrafluoroethylene filter paper with smaller aperture has stronger resistance to partial discharge and higher AC insulation breakdown strength, which can greatly improve the insulation reliability of the high temperature superconducting cable.