In　this　work,　hydrogen　diffusion　behavior　and　mechanisms　in　the　4130X　steel　influenced　by　temperature,　locally　high　concentration,　and　grain　boundary　were　studied　by　leveraging　both　electrochemical　hydrogen　permeation　experiments　and　molecular　dynamics　simulations.　It　was　revealed　that　the　hydrogen　diffusion　coefficient　of　the　4130X　steel　was　increased　with　increasing　temperature　and　decreasing　locally　high　hydrogen　concentration.　The　grain　boundaries　with　misorientation　below　15　degrees　characterized　by　an　electron　backscatter　diffraction　map　were　identified　as　hydrogen　trapping　sites,　thus　rendering　a　lower　mean　square　displacement　of　hydrogen　atoms　and　localized　hydrogen　diffusion　trajectories.　Furthermore,　at　a　high　hydrogen　concentration　of　4　at.　%,　these　grain　boundaries　were　saturated　by　hydrogen　atoms,　and　platelet-like　hydrogen　clusters　were　formed　within　the　lattice,　which　further　inhibited　the　diffusive　motion　of　hydrogen　atoms.　These　findings　would　deepen　our　understanding　of　hydrogen　embrittlement　mechanisms　by　establishing　the　connections　between　macroscopic　permeation　behavior　and　atomic-scale　hydrogen　diffusion　in　structural　materials.