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Abstract: This paper proposes an optimal real-time energy management strategy based on the Pontryagin's Minimal Principle (PMP) targeting at minimizing operation cost for a plug in proton electrolyte membrane (PEM) fuel cell city bus. The Dynamic Programming (DP) and PMP strategies are firstly deduced. Influences of the initial co-state value on the PMP strategy are analyzed. The DP, PMP, Charge Depleting Charge Sustaining (CDCS) and Blended strategies are compared in a simulation model. Results show that, major factors that influent the operation cost are the end value of battery State of Charge (SoC), the SoC trajectory curve, and the distribution of the working points of the fuel cell system. From a statistic viewpoint, the operation cost increases almost linearly with the end value of the SoC with a gradient of 1.41 Yuan.%−1. Compared with a CDCS strategy, the operation cost can be reduced by 7.2% through taking the DP strategy, and by 5.9% through taking the PMP strategy. The PMP strategy leads to an operation cost that is 1.4% higher than the DP, but it is applicable in the real-time control system. An online energy management strategy based on PMP was set up and applied to an embedded controller. Tests in the 30 “China city bus typical cycles” showed that, the fuel economy was 5.8 kg (100 km)−1, and the operation cost was 271.3 Yuan (100 km)−1. [Copyright &y& Elsevier]