CdS@C nanoparticles with different carbon content were successfully prepared by hydrothermal carbonization method, and the phase structure, morphology, optical, photoelectric chemistry and photocatalytic properties of CdS@C were studied. The experimental results show that the shell is successfully prepared as carbon layer, and the hexahedrite structure CdS is used as CdS@C particles in the core. The morphology of CdS@C particles is mainly spherical, with uniform particle size and good dispersion. XPS spectra confirm that the carbon loading on the surface of CdS@C particles mainly existe in the form of amorphous carbon. UV-Vis spectra show that the sensitization of surface carbon in CdS@C nanocrystals increase the visible light response range and narrowed the energy gap. PL show that the luminescence intensity of carbon-coated CdS@C nanoparticles is weaker than that of pure CdS, which effectively inhibited the electron-hole pair recombination. Transient photocurrent response and electrochemical impedance spectroscopy (EIS) indicate that CdS@C nanocomposite have a good optical response and show more efficient photocarrier separation and transfer efficiency. CdS@C nanocomposite exhibites good photocatalytic activity and stability under visible light radiation, and ·O2- and h+ play major roles in photocatalysis.