There have been many changes in Subway train types since SeoulMetro opened the Line No.1 in 1974. Propulsion control device has changed many times following the generations of control method from resistance control method which uses large resistor for the traction motor control to chopping control which uses power semiconductors and finally to inverter control. Railroad vehicle propulsion control device refers to devices such as converter/inverter which supply power for subway operation, power conversion equipment like small switching-mode power supply and traction motor. In this paper, we will analyze every part of railroad vehicle propulsion control device of SeoulMetro so we can find problems in the subway operation. And we will present propulsion control device model which makes minimized failures, efficient maintenance possible when replacing railroad vehicle later. By doing this, we hope to ensure stability and improve energy efficiency to the top.