Abstract: The diffusion and accumulation behaviour of hydrogen in X70 pipeline steel were investigated via hydrogen permeation test, hydrogen diffusion simulation, and hydrogen content test technology in a simulated coal gas environment (4 MPa total pressure, 0.2 MPa hydrogen partial pressure). The mechanical properties of the X70 pipeline steel substrate and weld in a simulated coal gas environment were also analyzed through impact toughness test, crack propagation test, notch tensile test, and slow strain rate tensile test. Experimental results show that hydrogen absorbed on the X70 steel surface in a simulated coal gas environment spreads into the inside of the X70 steel, and the internal diffusion hydrogen mass fraction is 1.9×10^-7 after reaching a steady state. Compared with the original performance in air, there is no decline in the impact performance, notched tensile and slow strain rate tensile strength, plasticity, and damage tolerance of the X70 pipeline steel substrate and weld in simulated coal gas. Results show that in a coal gas environment, X70 steel has a lower risk of hydrogen embrittlement.