The invention belongs to the technical field of composite electrode material preparation, and relates to a preparation method of a composite film electrode with CoZn-S nanoparticles inserted into graphene (rGO@CoZn-S) and application of the composite film electrode to a supercapacitor. The preparation method comprises the following steps: firstly, preparing a Co(NO3)2 solution and a Zn(NO3)2 solution and uniformly mixing and stirring the Co(NO3)2 solution and the Zn(NO3)2 solution in a volume ratio of 1: 2-2: 1, and adding a 0.4 mol/L 2-methylimidazole solution which is uniformly dispersed byultrasonic processing and carrying out uniform mixing to obtain CoZn-MOF turbid liquid; then, measuring the prepared CoZn-MOF turbid liquid and adding the measured CoZn-MOF turbid liquid into a graphene solution, carrying out standing and vacuum filtration to obtain a GO@CoZn-MOF sandwich-shaped composite film; and finally, ultrasonically dispersing thioacetamide and absolute ethyl alcohol uniformly, transferring the obtained solution to a reaction kettle and soaking the GO@CoZn-MOF composite film in the solution, keeping the reaction kettle under a constant temperature of 90-120 DEG C for 1-3hours, cooling to room temperature, taking out the sample and carrying out cleaning and drying in vacuum. The graphene is used as a substrate, so that the flexibility and conductivity of the materialare enhanced to a great extent; and meanwhile, CoZn-S nanoparticles derived from CoZn-MOF directly grow on the surface of the graphene in situ and can be used as an electrode material, thereby preventing the use of adhesives and conductive agents.