The invention provides a preparation method of a CdS/CoO nano-heterostructure and relates to the field of preparation methods of semiconductor composite materials, aiming at solving the technical problems of an existing catalyst of low solar energy conversion rate and high cost. The method comprises the following steps: firstly, immersing a CdS nano-rod into a methanol solution containing dimethylimidazole; hydrolyzing the dimethylimidazole by utilizing a trace amount of water in methanol, so as to form a partial alkaline environment on the surface of the CdS nano-rod; then adding a methanol solution of Co(NO3)2 into the solution to obtain a CdS/Co(OH)2 nano-composite material; finally, calcining in an inert atmosphere to obtain a CdS/CoO nano-heterostructure catalyst. The material provided by the invention sufficiently utilizes visible light under the condition that no noble metal material is used as a co-catalyst, and the conversion utilization rate of solar energy is increased; thematerial has very good photoresponse to a visible light region. The material can be used in water photolysis hydrogen production reaction.