It is crucial to construct an efficient catalyst with high activity and excellent selectivity for realizing CO₂ electroreduction reaction (CO₂ER) to high-value-added chemicals, especially the C2 products. Density functional theory (DFT) provides a powerful tool for investigating the promotional effect on C2 selectivity of finely tuned catalyst structures, which is currently difficult to control using experimental techniques, such as interatomic distances. In the work, 5 Cu₂O catalyst models are constructed with different Cu-Cu atomic spacing (d_Cu-Cu). The results of DFT calculations show that adjusting the d_Cu-Cu can effectively tailor the electronic structures of active sites, enhance catalytic activity, and improve product selectivity. Specifically, the Cu atom pair spaced at d_Cu-Cu = 2.5 Å could optimize the adsorption configuration of *CO and enhance the binding strength of *CO, thus improving *CO adsorption energy and reducing the energy barrier of C-C coupling. The work proves the feasibility of spacing effect in enhancing the C₂H₄ selectivity of CO₂ER and provides a new idea for the catalyst modification for other reactions of polyprotons-coupled electrons.