Radial distribution functions (RDFs) of imidazolium-based ionic liquids were evaluated by adopting effective fragment potential version 2 - molecular dynamics simulation (EFP2-MD), whose force fields were defined by a set of simple ab initio quantum chemical calculations for each ionic fragment. It was found that EFP2-MD could reproduce RDFs of ion pairs much faster than ab initio MD without losing chemical accuracy. This means that EFP2-MD has a potential to predict and design thermodynamic properties of novel ionic liquids.