Effect of solvent at the water/solid interface plays a non-negligible role in chemical reactions. Explicit solvation has been proved for its important effect on thermodynamics and kinetics of catalytic reactions. However, systematic studies about this perspective are still absence. In this work, using the model of single platinum atom immobilized on the metal vacancies of a series of MXenes, we systematically investigate the implicit/explicit solvent effect on their catalytic performance of the hydrogen evolution reaction (HER). We find that the solvent effect plays a significant role in affecting the calculation results for some systems. For TiNbC–Pt, the value of ΔG decreases from −0.121 to −0.511 (−0.583) eV when considering implicit (explicit) correction, implying the decisive role of solvent effect for calculating HER in this system. Bader charge analysis and AIMD simulations reveal that TiNbC–Pt surface is sensitive to HO, thus causing this abnormal case. Surprisingly high-entropy phases of MXene overall are less sensitive to solvent compared to the pure phases, which could be due to their alloyed lattice with a strong ability against electronic and lattice fluctuations induced by solvent. Several systems like VC–Pt, TiMoC–Pt, and VNbC–Pt are predicted to be excellent electrocatalysts for alkaline HER with the appropriate Gibbs free energy of hydrogen adsorption and kinetic barrier of water dissociation. The perspective exemplified in this work highlights that more feasible operando should be considered, e.g., influence of water, to better simulate the reaction process. Our work suggests that Pt-doped MXenes are perfect systems for hosting atomic catalyst as well.