23%。In the research of optimal operation line control strategy of parallel hybrid electric vehicle (PHEV), engine is often considered as the primary object. It can improve vehicle's fuel economy with engine working on optimal operation line, but motor's operation efficiency is not always the best. Motor, as another power source of HEV, was the primary object. The motor optimal efficiency line was designed, and the corresponding control strategy was established subsequently. Contrasted with the simulation results of the logic threshold value control strategy, motor optimal operation line control strategy could decrease vehicle's fuel economy by 9.5%, and could increase motor's operation efficiency by 23%.