Three-dimensional classical density functional theory (CDFT) has been introduced and applied to predicting gas separation in metal-organic frameworks (MOFs). The formula of CDFT is based on modified fundamental measure theory (MFMT) and mean field approximation (MFA). The accuracy of the theory has been examined by simulations, and it has been implemented into a high-throughput screening of CH4/H-2 separation materials. A total of 1200 MOFs have been examined, with selectivity ranging from 70 to 220 depending on the temperature, pressure and bulk CH4/H-2 ratio, which is much higher than that of real MOFs. A set of promising CH4/H-2 separation MOFs has been identified. According to the analysis of the isotherm and density profile, a MOF material with a pore size that can accommodate only one CH4 molecule seems to be the best for CH4/H-2 separation. (C) 2016 Elsevier Ltd. All rights reserved.