Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymers with wide range of potential applications. However, the availability of three-dimensional (3D) COFs is still limited, and their synthesis is confined to the high-temperature solvothermal method. Here, we report for the first time a general and simple strategy to produce a series of 3D ionic liquid (IL)-containing COFs (3D-IL-COFs) by using IL as a green solvent. The syntheses are carried out at ambient temperature and pressure accompanied by a high reaction speed (e.g., only three mins for 3D-IL-COF-1), and the IL can be reused without activity loss. Furthermore, the 3D-IL-COFs show impressive performance in the separation of CO2/N2 and CO2/CH4. This research thus presents a potential pathway to green large-scale industrial production of COFs.