Two classes of new characteristic parameters based on Pontryagin's minimum principle were proposed for the energy management optimization of plug-in hybrid electric buses and were used to build a driving condition database,in which non-equilibrium state characteristic parameters were related to the speed-torque distribution and equilibrium state characteristic parameters were related to the optimal control.A data-driven optimal equivalence factor estimation method with correction capability was also proposed and a data-driven energy management strategy was built through the driving condition similarity in the stage of charge sustaining,which is a key stage for the fuel consumption of buses.The results show that the strategy can make the equivalence factor and SOC (state of change) trajectory of different trips be close to the optimal.The new strategy improves the fuel economy by about 5.72% comparing with the rule-based strategy,and it can overcome the difficulty in accurately predicting future driving conditions.