Transition steel sulfides (TMSs) are promising electrocatalysts for hydrogen evolution response (HER), whereas TMSs often undergo from inevitable floor oxidation in air, and the affect of the floor oxidation on their HER catalytic exercise stays unclear. Herein, we exhibit an efficient technique for lowering the floor oxidation diploma of simply oxidized CoS2 by introducing glued vanadium pentoxide (V2O5) nanoclusters, profiting from the preferential adsorption and powerful interplay between high-valence V and O2. Mixed oxidation safety and elaborate oxidation management experiments reveal that diminished floor oxidation diploma of CoS2 is conducive to affording promising HER catalytic efficiency, because the oxidized floor of CoS2 can hinder the dissociation of water and thus is dangerous to the HER course of. Direct proof is offered that floor oxidation must be fastidiously thought-about for TMS-based HER catalysts. The current work not solely develops a brand new technique for safeguarding CoS2 from floor oxidation, but additionally supplies deep perception into the affect of floor oxidation on the HER efficiency of transition steel compounds.