This paper discusses the effects of different engine control methods on vehicle performance using a compact range extender-type PHV with a series-hybrid system. Vehicle performance was analyzed and compared in detail using two typical engine control methods: the variable control method, which drives the engine in accordance with the vehicle load, and the constant control method, which drives the engine at a constant maximum load efficiency. Specifically, by evaluating the performance in both driving tests by a test vehicle and driving simulations, we identified the characteristics of each engine control method and confirmed which is superior in terms of the seven PHV performance indices determined by the Japanese Ministry of Land Infrastructure and Transport. The comparison results quantitatively verified that the constant control reduced engine loss but caused battery loss to increase. However, since the best control method is determined by the engine and battery loss characteristics of the target vehicle, the constant control method enables superior mileage for the vehicle examined in this research due to its large engine loss reduction effect. In our case, 7.9% improvements of the charge sustaining mode mileage FCS and 7.6% improvements of the combined mileage FPH have been achieved by adopting the constant control method.