Capturing CO2 from the flue gases for sequestration is currently a key issue in environmental protection. Metal-organic frameworks (MOFs) are a new class of porous materials and have shown great promise for CO2 adsorption and separation applications. While the linkers of MOFs influence the CO2 adsorption performance greatly, the mechanism about it is still not clear. In this work, density functional theory calculations were performed to study CO2 adsorption mechanism on linker of isoreticular metal-organic framework-1 (IRMOF-1). The effect of model sizes was investigated by comparing the adsorption energies of different models with CO2 located on the same adsorption sites. The results indicate that model (HCOO)(5)Zn4O(BDC)Zn4O(HCOO)(5) is sufficient to calculate CO2 adsorption on linker of IRMOF-1. Eight different positions on linker of IRMOF-1 with three orientations of CO2 were studied in detail to understand the mechanism of CO2 adsorption. The side position with CO2 parallel attack at hydrogen side of linker edge is the most favorite adsorption site. The effects of chemical modifications on CO2 adsorption were studied, and the adsorption energies were found to be significantly increased. This work will be helpful to design and synthesis new materials that have higher CO2 adsorption abilities. (C) 2011 Elsevier Ltd. All rights reserved.