It is well known that the low-valent Cu species are important catalytically active centers in the reduction of CO₂ to hydrocarbon products. However, the Cu(I)-based catalysts are easily reduced during the electroreduction of CO₂, which causes phase transformation of catalysts and leads to a decrease of intrinsic catalytic activity. Therefore, it is of great significance to synthesize Cu(I)-based catalysts with specific interactions that can keep the catalytically active Cu sites stable in the electrocatalytic process. Based on the above considerations, a hexanuclear Cu cluster with strong cuprophilic interactions has been designed and utilized as a secondary building unit (SBU) to construct a stable metal-organic framework (MOF) electrocatalyst (NNU-50). As expected, the NNU-50 has served as an effective electrocatalyst for the CO₂-to-CH₄ conversion by exhibiting a high Faradaic efficiency for CH₄ (FE ${}_{{\mathrm{C}\mathrm{H}}_4}$) of 66.40% and a large current density of ~ 400 mA·cm⁻² at −1.0 V vs. reversible hydrogen electrode (RHE), which is one of the best catalytic performances among the stable MOF electrocatalysts until now. This work contributes more ideas for the design of stable and efficient MOF-based electrocatalysts for CO₂ reduction reaction.