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This paper presents the electric power system analysis and design of an expanding steel cogeneration plant. The site and capacity of shunt capacitor banks as well as the tap position of transformers are determined according to the power flow analysis. Also, to comply with the restriction of circuit breaker capacity, the high-impedance transformers are designed. In addition, the voltage fluctuation resulted from the dramatic reactive power variation of hot strip rolling mill can be greatly reduced if proper static var compensator is installed. The significant voltage sag due to the starting of induction motor can be effectively improved by applying wye-delta transformer starter. Furthermore, the total voltage harmonic distortion and the total current demand distortion are both acceptable if the proper filters are installed. It is also found that the cogeneration system can keep stable operation in autonomous mode by applying the governor control action and the load-shedding scheme after tie line tripping. It is concluded that the power system analyses are important for the steel plant with cogeneration unit to identify hidden problems and remedy strategy to ensure the system power quality and operation performance.