Abstract: Flexible hoses are key equipment in the development of marine resources. During the transportation of oil and gas, the small gas molecules such as CH₄, CO₂, H₂S and steam in inner pipes will gradually penetrate into the internal pressure sheath, which will seriously threat the service safety of flexible hoses. In order to ensure the flexible hoses run safely and stably, and to explore the methane permeation rule, the methane penetration test was conducted at the normal temperature with High Density Polyethylene(HDPE) prototype hoses. The results show that: (1) The permeation behavior of methane in the new HDPE pipe material can be roughly divided into three stages, i.e., the dissolution and diffusion period, the slow desorption period and the rapid desorption period, at a time ratio of 1:6:5, and the average gas permeability in the second stage is one third of that in the third stage.(2) After the saturation and dissolution of methane molecules in HDPE material, the annular pressure and the gas permeability are in the relationship of negative exponential function.(3) The supercritical permeability characteristics of methane are found, specifically, the gas permeability peaks when the test pressure is close to the critical pressure of methane. When the test pressure is lower than the critical pressure, the greater the test pressure, the greater the gas permeability.However, when the test pressure is higher than the critical pressure, the greater the test pressure, the smaller the gas permeability. Generally, the research results could provide reference for the application of flexible hoses in the offshore oil and gas development project, as well as the research and development of new materials.