In this paper, 48V MHEV vehicle with P0 + P4 structure is studied. In the previous paper, the best fuel economy was obtained when the energy obtained by regenerative braking was used only for EV driving. In an actual driving environment, a power generating function by an engine is essential. Therefore, not only regenerative braking energy but also additional energy from power generation is used for EV travel. Finally, the fuel economy is evaluated according to the amount of generating energy and control tendency of generating.