In this paper, an energy management strategy is proposed for a series plug-in hybrid electric vehicle. A number of quadratic equations are employed to determine the engine fuel-rate with respect to battery power. The problem is solved by using quadratic programming and simulated annealing method together to find the optimal battery power commands and the engine-on power. The influences induced by the inertias of the engine and generators are analyzed to improve the calculation precision. In addition, the state of health of the battery is taken into account to extend the application of the proposed method. Simulations were performed to verify that the proposed algorithm can decrease fuel consumption of plug-in hybrid electric vehicles.