As one of the main greenhouse gases and a kind of important "potential carbon resources", CO2 has received people's widespread attention. The CO2 separation can be achieved via conventional methods, such as pressure swing adsorption, dry and wet amine scrubbing, and cryogenic distillation etc. However, all these methods will require high cost. The membrane technology could offer the opportunity to meet the demand for high energy efficiency, lower cost, and operation simplicity for gas separation. It has been found that the polymer membranes containing CO2-favored organic units show outstanding CO2 separation performance due to the unique affinity between CO2 and the units. Thus, it is highly important to extensively explore novel CO2-favored organic units and investigate the effects of CO2-favored organic units on gas separation. In this review, the CO2-favored organic units recently utilized for fabricating CO2 separation membranes have been reviewed. The development of the CO2- favored organic units in CO2 separation membranes in the future has also been prospected.