Fundamental understanding of the dependence between the structure and composition on the electrochemical CO2 reduction reaction (CO2RR) would guide the rational design of highly efficient and selective electrocatalysts. A major impediment to the deep reduction CO2 to multi‐carbon products is the complexity of carbon–carbon bond coupling. The chemically well‐defined catalysts with atomically dispersed dual‐metal sites are required for these C−C coupling involved processes. Here, we developed a catalyst (BIF‐102NSs) that features Cl− bridged dimer copper (Cu2) units, which delivers high catalytic activity and selectivity for C2H4. Mechanistic investigation verifies that neighboring Cu monomers not only perform as regulator for varying the reaction barrier, but also afford distinct reaction paths compared with isolated monomers, resulting in greatly improved electroreduction performance for CO2. Chemically well‐defined catalysts with atomically dispersed dimer‐copper sites are elaborated to modulate the reaction path of CO2 electroreduction reaction (CO2RR). The BIF‐102NSs catalyst with Cl− bridged dimer copper (Cu2) units shows higher catalytic activity and selectivity for C2H4, because the neighboring Cu monomers perform as regulator for varying the reaction barrier and afford distinct reaction paths compared with isolated monomers.