The g-C₃N₄ nanosheets are prepared by thermal polymerization method using melamine as the raw material. Then CdS nanoparticles are grew by the chemical bath deposition， which in turn construct the g-C₃N₄/CdS heterostructures successfully. The scanning electron microscope， X-ray diffractometer and X-ray photoelectron spectroscopy are applied to characterize the morphology， crystal structure and chemical composition of samples. It is shown that the CdS nanoparticles with hexagonal wurtzite structure are uniformly attached to the surface of g-C₃N₄ nanosheets. The g-C₃N₄/CdS photodetector has a better photoresponse to ultraviolet light at zero bias voltage， and its photocurrent value is about 8 times higher than that of the g-C₃N₄ nanosheet photodetector. Moreover， the g-C₃N₄/CdS photodetector also displays well light response in the visible light region， and shows stability and cyclicity of detection to blue and green light.