In this paper, a novel energy management strategy for plug-in hybrid electric vehicles (PHEVs) is proposed, considering engine on/off control and state-of-charge (SOC) trajectory planning. First, the powertrain structure is analyzed in detail, and then the fuel rate is fitted versus the battery power by a series of quadratic equations. Pontryagin's minimum principle is employed to determine the optimal engine on/off switching and battery power commands, and the estimation distribution algorithm is applied to search for the optimal equivalent factor. Numerical simulations and hardware-in-the-loop experiments validate that near-optimal fuel performance can be achieved based on the proposed algorithm with reasonable computational cost. In addition, the SOC reference trajectory optimized by the proposed algorithm is validated to be effective for application with online energy management strategies. (C) 2018 Elsevier Ltd. All rights reserved.