Hydrogen embrittlement causes metals exposed to H-containing environments to become brittle and crack, posing serious risks to industries such as energy, manufacturing, transportation, and aerospace. Understanding the interaction between hydrogen and steel is crucial for addressing hydrogen embrittlement challenges. This study uses first-principles methods based on the density functional theory to examine how different alloying elements influence the dissolution of H atoms in α-Fe-based solid solutions, both with and without vacancy defects. The interactions between H atoms and alloying elements, as well as Fe atoms are analyzed using crystal orbital Hamilton populations. Additionally, the climbing image-nudged elastic band (CI-NEB) method was used to calculate the influence of the alloying elements on the diffusion of H atoms in α-Fe-based solid solutions. The results indicate that H atoms preferentially dissolve in the second and third nearest tetrahedral interstitial sites of alloy atoms. The solution enthalpy of H atoms is determined by the bond strength between the H atom and the nearest alloy atom as well as Fe atoms. For systems with vacancy defects after alloying, the solution enthalpies of H atoms at the first nearest vacancy for elements, such as Sc, V, Cr, Mn, Co, Ni, and Cu are lower than those at the tetrahedral interstitial sites of the complete α-Fe-based solid solutions. However, the opposite effect is observed for systems containing Al, Si, Ti, Zr, Nb, Eu, and W. Furthermore, alloying with Ti, Cu, Zr, Nb, and rare-earth elements increases the diffusion energy barriers for H atoms moving from the second nearest tetrahedral interstitial site to the third nearest site, while reducing diffusion energy barriers in the opposite direction. Conversely, the opposite effects are observed in α-Fe-based solid solutions containing Si, V, Cr, Mn, Co, Ni, Mo, and W.