The invention relates to a nickel sulfide-cadmium sulfide nanowire heterostructure and a preparation method thereof and belongs to the technical field of preparation of new energy materials. According to the composite material provided by the invention, the main body is the cadmium sulfide nanowire, and dentritic beta-NiS sheets are attached to the surface. The material has excellent capacity of performing visible catalytic decomposition on water to produce hydrogen. The preparation method comprises the following steps: preparing the cadmium sulfide nanowire by a solvent thermal process; taking the obtained cadmium sulfide nanowire as a template, taking nickel acetate as a nickel source, taking thiourea as a sulfur source, taking sodium hypophosphite as a reducing agent, uniformly growing beta-NiS nanosheets on the surface of cadmium sulfide in a hydrothermal environment, thereby obtaining the nickel sulfide-cadmium sulfide nanowire heterostructure with tight combination and dispersing uniformity. The product obtained by the method is high in yield, high in purity and controllable in morphology and does not need after-treatment; and moreover, the method has the advantages of simplicity in equipment and process, strict and controllable synthetic growth conditions, high product yield, low cost, clean and environmental-friendly production process and the like.