The invention discloses a preparation method of a p-CoO / n-CdS / TiO2 composite semiconductor photocatalyst, which comprises the steps of: firstly, with ammonium salts, cadmium salts, thiourea and deionized water as raw materials, sequentially carrying out microwave reaction, ultrasonic dispersion, heating reaction ,washing, ultrasonic dispersion, filtering, drying, roasting, grinding and other treatments to obtain solid CdS powder; secondly, with the solid CdS powder, cobalt salts, ammomia water and deionized water as raw materials, sequentially carrying out reaction, ultrasonic dispersion, reduced pressure distillation, washing, ultrasonic dispersion, filtering, drying, roasting, grinding and other treatments to obtain solid p-CoO / n-CdS powder; and thirdly, with the solid p-CoO / n-CdS powder, tetrabutyl titanate, absolute alcohol, hydrochloric acid and deionized water as raw materials, sequentially carrying out reaction, ultrasonic dispersion, reduced pressure distillation, washing, ultrasonic dispersion, filtering, drying, roasting, grinding and other treatments to obtain the p-CoO / n-CdS / TiO2 composite semiconductor photocatalyst; thus, the photo-corrosion speed of the CdS is effectively decreased, and the photocatalysis efficiency of the p-CoO / n-CdS / TiO2 is increased. The preparation method has simple and convenient processes, is practical and feasible, and is beneficial to popularization.