This paper introduced a new power flow control strategy for a variable speed engine-generator based range-extended electric vehicle. The specific fuel consumption map of the internal combustion engine (ICE) has been obtained by off-line experiments to achieve optimal fuel efficiency. Finally, a typical range-extended electric vehicle is modeled and investigated such as acceleration traversing ramp, maximum speed, fuel consumption and emission are performed on the dynamic model of a range-extended electric vehicle. The energy consumption and cost were compared to tradition range-extended electric vehicle. Computer simulation results obtained, confirm the validity and performance of the proposed power flow control approach using for series hybrid electric vehicle.