With the rapid development of hydrogen energy industry and the urgent need for safe storage and transportation of hydrogen, it has become a major trend to utilize the existing long-distance natural gas pipelines for hydrogen transportation. However, blending hydrogen into natural gas pipelines can adversely impact pipeline steel, posing new problems and challenges for the safe transportation. Herein, the mechanical behavior of X80 pipeline steel in atmospheres of hydrogen blended methane was assessed via in-situ slow-rate tensile test, gas-phase hydrogen permeation test and hydrogen content measurements. The main concern lies in that the effect of different hydrogen-blending ratios on the mechanical properties, hydrogen permeation behavior and the hydrogen content of X80 steel at a temperature of 298 K, along with the impact of temperature on the kinetic parameters of gas-phase hydrogen permeation by the hydrogen-blending ratio of 10%. Results indicated that as the hydrogen-blending ratio increases, the yield and tensile strength of X80 pipeline steel decreased slightly, while the elongation at break decreased gradually, and both the hydrogen embrittlement sensitivity index and the hydrogen permeability coefficient and diffusion coefficient increased. The hydrogen permeability and diffusion coefficients increase with the increase of temperature under the condition of 10% hydrogen doping ratio. At temperatures between 298 K and 373 K, the hydrogen diffusion activation energy and permeation activation energy of X80 pipeline steel were 1.56 and 11.25 kJ/mol, respectively.