Electrochemical CO2 reduction (ECR) to value-added products using renewable electricity enables artificial carbon cycle and clean energy storage, which represents an important strategy to realize carbon neutrality. Copper-based catalysts have been recognized as the only materials that can realize the electrochemical reduction of CO2 to produce a variety of products. However, it faces the challenges of high overpotential and poor products selectivity in ECR. To promote the ECR performance of copper-based catalysts, template-assisted hydrothermal synthesis method was employed to synthesize CuO nanostructures, and the influence of the content of polyvinylpyrrolidone (PVP) template on the structure and ECR performance of CuO catalysts was demonstrated. The results indicate that the nucleation and growth of CuO crystals in hydrothermal synthesis can be affected due to the addition of PVP. The average particle size and ECR performance of the CuO catalysts depends on the content of the PVP template. The hydrophobic carbon chain in PVP endows the molecule with repulsive force, which has retarded the agglomeration of CuO nanostructures. With the increase in PVP content, the average particle size decreases first and then increases, while the ECR performance increases first and then declines. The desired CuO-PVP-25 catalyst with 25% PVP content shows the minimum average particle size of 29.53 nm. Under the given potential of -0.53 V，the CO selectivity and current density of CO2 electrochemical reduction products can reach up to 48.2% and -5.8 mA/cm2. The excellent ECR performance is associated with the particle size effect, as catalyst with minimized particle size offers more undercoordinated sites, which affects the binding energy of the catalyst surface towards the adsorption of the *CO intermediate, thus significantly affecting the catalytic activity and products selectivity.