Covalent organic frameworks (COFs) mixed matrix membranes (MMMs) combining individual attributes of COFs and polymers are promising for gas separation. However, applying COF MMMs for propylene/propane (C3H6/C3H8) separation remains a big challenge due to COF inert pores and C3H6/C3H8 similar molecular sizes. Herein, the designed synthesis of a Cu(I) coordinated COF for membrane C3H6/C3H8 separation is reported. A platform COF is synthesized from 5,5′‐diamino‐2,2′‐bipyridine and 2‐hydroxybenzene‐1,3,5‐tricarbaldehyde. This COF possesses a porous 2D structure with high crystallinity. Cu(I) is coordinated to bipyridyl moieties in the COF framework, acting as recognizable sites for C3H6 gas, as shown by the adsorption measurements. Cu(I) COF is blended with 6FDA‐DAM polymer to yield MMMs. This COF MMM exhibits selective and permeable separation of C3H6 from C3H8 (C3H6 permeability of 44.7 barrer, C3H6/C3H8 selectivity of 28.1). The high porosity and Cu(I) species contribute to the great improvement of separation performance by virtue of 2.3‐fold increase in permeability and 2.2‐fold increase in selectivity compared to pure 6FDA‐DAM. The superior performance to those of most relevant reported MMMs demonstrates that the Cu(I) coordinated COF is an excellent candidate material for C3H6 separation membranes.