In this work, quantum mechanical calculations and grand canonical Monte Carlo simulations were performed to study H-2 and CH4 uptakes as well as CO2 separation from CH4 or H-2 in MOF-205 with different modification approaches. Upon C48B12 impregnation and Li decoration, B-doped MOF-205 shows remarkably improved gas adsorption and separation performances. Under ambient condition, both H-2 and CH4 storage capacities in the modified materials meet the targets set by the US Department of Energy. Moreover, Li doping greatly increases the separation selectivity of CO2 in CO2/CH4 and CO2/H-2 mixtures. This multiple modifications strategy opens the door to the production of porous nanomaterials with higher gaseous adsorption and separation capabilities.