In order to meet the requirements of new thermal insulation materials for the steam pipeline of nuclear submarine， a new kind of thermal insulation structure based on polyimide foam was designed and manufactured for the surface of submarine steam pipeline. The thermal insulation performance and structural stability of the thermal insulation structure during use were studied according to the application requirements of submarine steam pipeline. The thermal insulation mechanism was also investigated. The results indicate that the external surface temperature of the insulation structure is 45.2 to 46.5 ℃ during the continuous heating at 280 ℃ for 480 hours. Furthermore， it is also found that the structural and dimensional deformation is almost 0 during the continuous heating test and the subsequent static test for 720 hours. It is noteworthy that the multi-layer polyimide foams applied as insulation structure of steam pipeline can solve the processing and environmental problems related to the inorganic rock cotton system. The data in this paper will provide technical and practical support for the practical application of polyimide foams on steam pipeline surface.