The invention provides a preparation method of a nickel-cobalt bimetallic sulfide/rGO composite electrode material, and the method comprises the following specific steps: 1) performing pretreatment: cleaning a conductive substrate, and drying the conductive substrate for later use; 2) preparing electro-deposition solution: dissolving nickel salt and cobalt salt in deionized water, adding thiourea,and stirring the liquid until the nickel salt and the cobalt salt are dissolved, adding graphene oxide, and performing ultrasonic dispersion to obtain electrodeposition solution; 3) performing electrodeposition: taking the conductive substrate as a working electrode, taking a saturated Ag/AgCl electrode as a reference electrode, taking a platinum sheet as a counter electrode, and carrying out electrodeposition by adopting a constant potential method or a constant current method; 4) preparing the composite electrode material: cleaning the electrode obtained by deposition with absolute ethyl alcohol and deionized water, and performing drying to obtain the NiCo2S4/rGO composite electrode material. The preparation method has the advantages of short flow, simple process and low cost, can be applied to a super capacitor, and has excellent capacitive performances.