Abstract: In order to convert a battery electric vehicle into an extended-range electric vehicle, by analyzing the working patterns and principles of range extender, parameters of engine and generator of the range extender's were matched, and reasonable design parameters were obtained. With the co-simulation platform of MATLAB/ Simulink and ADVISOR, the battery electric vehicle and the extended-range electric vehicle were simulated in the same driving cycle (CYC_UDDS) respectively. Simulation results show that the driving range of the extended-range electric vehicle reaches 177.8 km, meanwhile its dynamic performance and fuel efficiency can be controlled within an appropriate range, which indicates that the modification scheme is reasonable and effective, and it provides the reference for the transformation test and vehicle road test.