The growing concerns over the energy crisis and climate change have led to increasing demands for fuel economy in automobiles, which has accelerated the adoption of the (Pulse-and-Glide) PnG mode as a energy-saving technology based on speed control. While numerous studies have validated the energy-saving potential of the PnG mode, there is still a lack of quantitative analysis and identification of the key factors influencing its energy-saving performance, as well as optimization strategies for the PnG mode. This study uses a specific vehicle model as the subject, establishing a coupled simulation platform with CarSim and MATLAB/Simulink. The energy-saving effects of the PnG mode are analyzed through various control variables. The results show that, compared to the constant speed mode, the PnG mode achieves significant energy-saving in the low-to-medium speed range, with the energy-saving effect diminishing as the average speed increases. Additionally, idle fuel consumption is identified as one of the key factors affecting the energy-saving performance of the PnG mode. Therefore, during the G-phase, it is recommended to disengage the transmission system from the wheels and ensure that the engine stops fuel consumption, thereby maximizing the energy-saving effect of the PnG mode.