•Hydrogen alloying with a proper concentration makes equiatomic FeCrNiMnCo alloy resistant to hydrogen embrittlement.•Hydrogen at the interface is the essential cause of the change in the mechanical properties of the material.•Hydrogen promoting the formation of nanotwins/stacking faults in high-entropy alloy.•The diffusion barrier of hydrogen in the high-entropy alloy and 316NG stainless steel were very close. This study reports the effect of hydrogen behaviors on the tensile properties of an equiatomic FeCrNiMnCo high-entropy alloy. We reveal that the hydrogen at the interfaces (including grain boundaries and twin boundaries, etc.) is the main factor affecting the mechanical properties of the materials. We found that hydrogen alloying with a proper concentration makes the alloy resistant to hydrogen embrittlement and improves the strength and ductility of the material. This beneficial effect is positively correlated with the hydrogen concentration at the interface of the alloy, with hydrogen promoting the formation of stacking faults / nanotwins, which are excessively compensatory to the surface cracks introduced by the hydrogen. The influence of hydrogen at the interface of 316NG stainless steel on the tensile behavior has also been discussed. Although hydrogen embrittlement occurred at the same hydrogen-charged conditions, the deterioration of the ductility of the deformed 316NG with a high hydrogen concentration at the interface was significantly reduced. AIMD simulation has been used to study the diffusion of interstitial hydrogen in the HEA and FeCrNi model alloy. It was found that the diffusion barrier and diffusion coefficient of hydrogen in the two alloys were very close at different temperatures.