Introducing large-scale plug-in electric vehicle（PEV） into a power system would produce extensive impacts on power system planning， operation as well as electricity market development. Hence， it appears necessary to properly control the PEV charging and discharging behaviors. A new unit commitment model and a solving approach are developed with the optimal PEV charging and discharging controls taken into account， and the objective is to minimize a combination of the operating cost as well as CO2emission amount of generators. A 10-unit 24-hour unit commitment problem is employed to demonstrate the feasibility and efficiency of the developed model and approach， and the impacts of the wide applications of PEV on the operating costs as well as the emission amounts of the power system examined. In addition， the impacts of different PEV penetration levels in the power system and different PEV charging modes， i.e. fully controlled charging mode， uncontrolled charging mode， delayed charging mode and continuous charging mode， on the results of the unit commitment problem are investigated.