Strategies that enable simultaneous morphology‐tuning and electroreduction performance boosting are much desired for the exploration of covalent organic frameworks in efficient CO2 electroreduction. Herein, a kind of functionalizing exfoliation agent has been selected to simultaneously modify and exfoliate bulk COFs into functional nanosheets and investigate their CO2 electroreduction performance. The obtained nanosheets (Cu−Tph−COF−Dct) with large‐scale (≈1.0 μm) and ultrathin (≈3.8 nm) morphology enable a superior FECH4 (≈80 %) (almost doubly enhanced than bare COF) with large current‐density (−220.0 mA cm−2) at −0.9 V. The boosted performance can be ascribed to the immobilized functionalizing exfoliation agent (Dct groups) with integrated amino and triazine groups that strengthen CO2 absorption/activation, stabilize intermediates and enrich the CO concentration around the Cu active sites as revealed by DFT calculations. The point‐to‐point functionalization strategy for modularly assembling Dct‐functionalized COF catalyst for CO2 electroreduction will open up the attractive possibility of developing COFs as efficient CO2RR electrocatalysts. A kind of functionalizing exfoliation agent has been selected to simultaneously modify and exfoliate bulk COFs into functional nanosheets and the obtained materials can be applied in highly selective CO2 electroreduction into CH4.