Surface defect engineering is an effective approach for manipulating the electronic structure for enhancing photocatalytic hydrogen evolution reaction (HER) activities. The surface electronic structure of ZnIn 2 S 4 (ZIS) nanosheets was modified by introducing and regulating surface sulfur vacancies (S V ) through Ar-plasma treatment in this work. Optimized ZIS photocatalysts with surface S V deliver a high HER rate of 261.9 μmol•h −1 under visible light (λ > 420 nm), approximately 2.06-fold higher than that of the original ZIS. Significantly, the AQE value reaches 51.2% under 420 nm monochromic light irradiation. A series of characterization analyses prove that S V only exists on the ZIS surface. Furthermore, H 2 O-FTIR demonstrated that surface S V is more conducive to the adsorption of H 2 O molecules. Additionally, density functional theory calculations clarify the disparity in the kinetic process of H 2 evolution under the alkaline state over ZIS with/without S V . Therefore, Ar-plasma treatment is a beneficial method for regulating the surface S V on ZIS nanosheets, improving the efficiency of the photocatalytic HER.