Covalent organic frameworks (COFs) membrane shows great potential for applications in gas storage and separation. In this work, the COF-5 nanosheet was synthesized via a facilely sonochemical method, which shows the high CO2 uptake capacities because of its unique structure. Then, COF-5 was dispersed in Pebax-1657 matrix to fabricate the mixed matrix membranes (MMMs), the resulting MMMs exhibits an enhanced CO2 permeability. Remarkably, the MMM that consists of 0.4 wt% COF-5 filler shows the highest CO2 permeability (similar to 493 Barrer). Furthermore, compared with the pristine Pebax-1657 membrane, the MMMs with COF-5 could impove the CO2/N2 selectivity (from 31.3 to 49.3), which almost surpassing the Robeson bond (2008). It is worth mentioning that the MMMs have stable operating performance during 120 h.