The invention discloses a method for preparing a p-CoO/n-CdS compound semiconductor photocatalyst, which comprises the following steps: in a ratio of the weight percentage of ammonium salt to cadmium salt to thiocarbamide to deionized water of (0.001 to 90 percent): (0.001 to 70 percent): (0.001 to 90 percent): (0.001 to 90 percent), mixing the ammonium salt, cadmium salt, thiocarbamide and deionized water for reaction, filtering, washing, roasting and grinding to obtain CdS solid powder; and in a ratio of the weight percentage of CdS solid powder to cobalt salt to ammonia water to deionized water of (0.001 to 90 percent): (0.001 to 70 percent): (0.001 to 90 percent): (0.001 to 90 percent), mixing the cobalt salt, ammonia water and deionized water for reaction, adding the CdS solid powderfor three times, and performing stirring, ultrasonic dispersion, distillation at reduced pressure, heat treatment, washing, filtering, roasting and grinding to obtain the p-CoO/n-CdS compound semiconductor photocatalyst by. The prepared p-CoO/n-CdS compound semiconductor photocatalyst can be applied to photocatalytic degradation of organic pollutants, photocatalytic decomposition of water for hydrogen production and manufacture of solar cells under the condition that ultraviolet light, visible light and sunlight are used as light sources respectively.