The basic configuration and operation modes of the series extended-range electric vehicle were analyzed and a novel method for engine choice and fuel economy evaluation was proposed. A co-simulation platform was set up using Cruise and Matlab/Simulink to evaluate the rule-based engine onoff and optimal operation line control strategies. The simulation results with typical driving cycles illustrate that, first, the engine on-off control strategy makes the engine and generator operate at their best efficiency points, and its fuel economy is better than that of the optimal operation line control strategy; secondly, when the optimal operation line control strategy is adopted in the extended-range mode, the engine downsizing will be beneficial and the extendedrange electric vehicle(E-REV) will achieve a better fuel economy and control effect.