Herein, we report the platinum-cobalt(x) (Pt-Co-x) nanoparticles (NPs) as a cocatalyst were synthesized by solvothermal method, and then modified on the surface of cadmium sulfide (CdS) via means of photoinduced deposition. Under visible light irradiation, the hydrogen generation rate of Pt3Co/CdS reached to 45.09 mmol.h(-1).g(-1) (QE = 46.01%, lambda = 420 nm), which was 2.7 times and 1.8 times higher than that of Co/ CdS and Pt/CdS, respectively. The high photocatalytic performance could be attributed to the strong synergistic effect between Pt and Co. Astoundingly, the photocatalytic activity was enhanced after the Pt-Cox NPs by acid treatment. The hydrogen production activity of Pt3Co-HNO3-5h/CdS was high up to 48.66 mmol.h(-1).g(-1) (QE = 54.36%, lambda = 420 nm), which was better than that of Pt3Co/CdS. It is proved that the enhanced photocatalytic activity was mainly due to the dealloyed Pt3Co NPs resulted in low coordination sites of Pt on the surface and provided more active sites, which enhanced the ability to capture photo-generated electrons, thus promoted the effective separation of carriers. In addition, XRD implied that Co atoms enter the Pt structure to form Pt-Co alloy phase. TEM showed that Pt-Co NPs has a polyhedral structure with size of about 13-15 nm. SEM/XPS revealed that Pt3Co NPs has been successfully decorated onto the surface of CdS. UV-Vis spectra of CdS nanoparticles interpreted its trait in visible light adsorption. PL spectra and I-T curves indicated that the Pt3Co-HNO3-5h/CdS and Pt3Co/CdS have higher electrons and holes separation efficiency.