As is well known that the specific capacitance of supercapacitors cannot be improved by increasing the mass of the deposited MnO₂ films, which means an appropriate deposition duration is important. In this study, nanobelt-structured MnO₂ films were prepared by the electrochemical deposition method under different deposition time to explore the effects of electrodeposition time change on the microstructure and electrochemical properties of this material. Benefiting from the microstructure of the MnO₂ films, the transfer properties of the charged electrons and ions were promoted. Meanwhile, a 3D porous nickel foam was chosen as the deposition substrate, which rendered an enhancement of the MnO₂ conductivity and the mass of the active material. The enhanced specific capacitance and specific surface area attributed to synergistic reactions. Subsequently, the electrochemical performances of the as-prepared materials were analyzed via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) tests. Results show that the optimum sample deposited for 50 s has a specific capacitance of 291.9 F g⁻¹ at the current density of 1 A g⁻¹ and lowest R_ct. However, its electrochemical stability cannot come up to the level of the 300 s sample due to the microstructure change.