This thesis is to investigate the power system operation strategy for an electrified mass rapid transit¡]MRT¡^network with the load transfer among main transformers by considering load growth and due to annual ridership increase, the loading factors of main transformers are improved so that the power system loss can be reduced. For the conventional planning of an electrified MRT system to serve the public transportation for the metropolitan area, the transformer capacity is often designed to meet the criterion of not only covering the peak demand but also providing the 100% fully capacity reserve for the system operation of target year. With such a high backup capability, the transformers are very lightly loaded for most of the operation time and significant core loss will be introduced over the lifecycle. In this thesis the train motion equation has been applied to find the mechanical power required, the proper strategy of unit commitment of main transformers and network reconfiguration by switching operation has been considered to enhance the operation efficiency of an MRT power system. To demonstrate the effectiveness of the proposed methodology, the Taipei MRT network is selected for computer simulation. It is found that the loading factors of main transformers can be improved dramatically and the load balance among the transformers can be obtained by the proper switching operation. An efficient strategy for transformer planning by taking into account the growth rate of load so that the overall investment cost of main transformers can be justified. The load characteristics and load growth rate of mass rapid transit¡]MRT¡^are derived by an Energy Management Model (EMM) and the AC load flow analysis is used to solve the transformer copper loss and core loss over the study period. To obtain optimal planning and operation strategy of main transformers for the MRT power system, the transformers initial investment cost and depreciation cost, peak power loss and energy loss, and reliability cost of distribution transformers are combined to form the overall cost function .By performing the dynamic programming (DP) the unit commitment of main transformers by considering the annual peak and off peak power loading of whole MRT system is derived. It is found that more efficient system operation can be obtained by the proposed methodology.