Traditional bulk MoS₂ as an effective H₂-evolution cocatalyst is mainly subjected to the weak hydrogen-adsorption ability of high-porpotion saturated S, resulting in a slow interfacial H₂-evolution reaction. In this paper, an efficient strategy for enhancing hydrogen adsorption of saturated S by manipulating electron density through O atoms is proposed to boost photocatalytic performance of CdS. Simultaneously, amorphization of MoS₂ can further increase the unsaturated active S sites. Herein, oxygen-contained amorphous MoS_x (a-MoOS_x) nanoparticles (10–30 nm) were tightly loaded on the CdS surface through a mild photoinduced deposition method by using (NH₄)₂[MoO(S₄)₂] solution as the precursor at room temperature. The photocatalytic H₂-evolution result showed that the a-MoOS_x/CdS performed the superior H₂-production activity (382 μmol·h⁻¹, apparent quantum efficiencies (AQE) = 11.83%) with a lot of visual H₂ bubbles, which was 54.6, 2.5, and 5.1 times as high as that of CdS, MoS_x/CdS, and annealed a-MoOS_x/CdS, respectively. Characterizations and density functional theory (DFT) calculations revealed the mechanism of improved H₂-evolution activity is that the O heteroatom in amorphous MoOS_x can enhance the atomic H-adsorption ability by manipulating the electron density to form electron-deficient S^(2−δ)− sites. This study provides a new idea to improve the efficiency and number of H₂-evolution active sites for developing efficient cocatalysts in the field of photocatalytic hydrogen evolution.