AbstractElectrochemical reduction of CO₂ to produce valuable multi‐carbon products is a promising avenue for promoting CO₂ conversion and achieving renewable energy storage, and it has also attracted considerable attention recently. However, the synthesis of Cu electrode with a controllable electrochemical active surface area (ECSA) to understand its role in CO₂ reduction to C₂H₄ remains challenging. Herein, a series of Cu electrodes with different ECSA is synthesized through a simple oxidation‐reduction approach. We reveal that the improved selectivity of C₂H₄ is proportional to the ECSA of Cu in the low ECSA range, and a further increase in ECSA has a negligible effect on its selectivity. The enlarged surface area could strengthen the local pH effect near the surface of Cu electrode and suppress the generation of C₁ products as well as H₂. The study provides a feasible strategy to rationally design electrocatalysts with high electrochemical CO₂ reduction performances.