The biochar was prepared from rice husk and modified with different concentrations of zinc acetate to produce products named RHC and MRHC, respectively. The prepared biochar was characterized by SEM, BET and XRD for its physicochemical properties. The analysis showed that the modified char had rich pore structure and large specific surface area, and the zinc existed on the surface of the biochar in the form of oxide particles. The rice husk biochar before and after modification was made into an electrode and its electrochemical properties were tested. The results showed that the specific capacitance of the modified carbon electrode was greatly improved, the resistance was significantly reduced, and the cycling performance and multiplicative performance were improved compared with the unmodified biochar. MRHC-0.3 (modified biochar at a zinc acetate concentration of 0.3 mol/L) had a specific surface area of 495 m2/g and a pore volume of 0.214 cm3/g. The capacitance retention rate of this electrode was 92.16% after 2000 charge/discharge cycles at 2 A/g. MRHC-0.3 electrode was used for electrosorption of Cu2+ at 0.9 V, pH 5. The MRHC-0.3 electrode was used for electrosorption of Cu2+, and the best adsorption effect was found at 0.9 V, pH 5, with the adsorption amount of 9.57 mg/g. The removal rate could reach 63.82% at 0.9 V, pH 5, and the initial mass concentration of Cu2+ of 50 mg/L.