The invention provides a preparation method for nickel-oxide/ reduced-graphene-oxide nanosheet composite materials. The preparation method includes using multiwalled carbon nanotubes as raw materials and adopting the Hummer method to obtain graphene-oxide nanosheets with lamellar structures and easy to disperse through oxidation; ultrasonically dispersing the grapheme oxide nanosheets and Ni (NO3)2 6H2O in ethyl-alcohol solvent to perform solvent thermal reaction at the temperature of 140-180 DEG C for 10-12 hours; after the temperature is cooled to room temperature, filtering, washing with water and absolute ethyl alcohol and drying in vacuum to obtain precursor composite materials; preforming thermal treatment on the precursor composite materials under air atmosphere and at the temperature of 200-250 DEG C for 3-5 hours to obtain the nickel-oxide/ reduced-graphene-oxide nanosheet composite materials. The composite materials prepared by the method integrate the characteristics of NiO and rCNGO, and are enabled to have better electrochemistry performance as compared with homogenous materials through synergistic effects among components, thereby being capable of serving as electrode materials of super capacitors.