A pumped-storage unit model is developed based on the conventional unit commitment model. According to the operating characteristics of pumped-storage units， virtual unit models for each operating mode as well as working state transition models are developed based on mixed integer programming principle. The IEEE RTS 96 system is used to test these models. The test results show that the proposed models can be easily combined with conventional unit commitment model， and it is effective to schedule the pumped-storage units and deal with the operating mode transition problem.