We report a bifunctional SBU-tuning strategy that simultaneously enhances the selective CO2 adsorption capacity of Cu-BTC and its structural stability under moisture. A series of Gly@Cu-BTCs were prepared by grafting glycine (Gly) to the secondary building units (SBUs) of the commercially available Cu-BTC through the nanoseed assistant ultrafast room temperature synthesis. N-2 isotherms evidenced higher BET specific surface area and pore volume of Gly@Cu-BTCs than that of Cu-BTC. Hence, Gly(0.3)@Cu-BTC exhibited a superior CO2 capacity of 5.4 mmol/g at ambient conditions, which is 12% higher than that of Cu-BTC. Besides, the adsorptive selectivity of Gly(0.3)@Cu-BTC for the equimolar CO2/CH4 and CO2/N-2 mixtures was separately up to 8.53 and 59.38, being 11% and 15% higher compared to that of Cu-BTC. More importantly, the stability of Gly(0.3)@Cu-BTC against moisture was improved. After 10 days(-1) exposure in 55% relative humidity, Gly(0.3)@Cu-BTC preserved 80% of its original CO2 capacity, while only 9% CO2 capacity remained for Cu-BTC. In addition, negligible CO2 capacity loss of Gly(0.3)@Cu-BTC was observed in the subsequent 10 days in moisture after the initial exposure. Gly(0.3)@CuBTC exhibited excellent regenerability, and its CO2 desorption efficiency reached up to 98% based on the consecutive adsorption-desorption cycles. The origination of the improved stability under moist of Gly(0.3)@CuBTC was interpreted with DFT calculation. The bifunctional SBU-tuning strategy demonstrated in this work enables the potential adsorptive separation application of Cu-BTC under moist working condition.