IGCC (Integrated Gasification Combined Cycle) power generation system can improve the utilization efficiency of coal and has less impact on the environment. Carbon capture and storage system (CCS) is an essential way to control greenhouse gas emission. This paper aims to study the combination of IGCC and CCS systems from the perspective of sustainability (in terms of environment). The model of IGCC and CCS systems are built in Aspen plus. Based on the model, the impact of oxygen-coal ratio to the performance of IGCC power generation system is studied. The results show that the mole fraction of CO and H2 could reach a relatively large value when the oxygen-coal ratio is in 0.7-0.8 and the net power of the system decreases with the oxygen-coal ratio. The emergy evaluation is performed by collecting the input and output data of the IGCC and IGCC-CCS systems under the oxygen-coal ratio of 0.8. The results show that the sustainability of the IGCC-CCS system is rising as the CO2 tax increases and the order of the sustainability with different CCS scale is relative to the CO2 tax. It indicates that the CCS system could improve the sustainability of the IGCC system under a certain CO2 tax by reducing the CO2 emission.