Three gas separation technologies, chemical absorption, membrane separation and pressure swing adsorption, are usually applied for CO2 capture from flue gas in coal-fired power plants. In this work, the costs of the three technologies are analyzed and compared. The cost for chemical absorption is mainly from $30 to $60 per ton (based on CO2 avoided), while the minimum value is $10 per ton (based on CO2 avoided). As for membrane separation and pressure swing adsorption, the costs are $50 to $78 and $40 to $63 per ton (based on CO2 avoided), respectively. Measures are proposed to reduce the cost of the three technologies. For CO2 capture and storage process, the CO2 recovery and purity should be greater than 90%. Based on the cost, recovery, and purity, it seems that chemical absorption is currently the most cost-effective technology for CO2 capture from flue gas from power plants. However, membrane gas separation is the most promising alternative approach in the future, provided that membrane performance is further improved.