The application efficiency of 48 V system was analyzed, including the fuel economy under different driving modes and driving cycles. The analysis focused on shift strategy, engine start-stop strategy, start and acceleration booster strategy, braking energy recovery and other energy management strategies. The results show that the mild hybrid function weakens in sport mode so that the driving experience is the same as that of traditional powertrain vehicle. In addition, the mild hybrid has 1 L/100 km higher fuel consumption rate than eco and normal modes. This exactly explains the influence of weight factor set by energy management application strategy of 48 V system on fuel economy at different modes. The battery SOC achieves dynamic balance in a complete legislation cycle, but decrease rapidly during the cold start. The fact that the initial power difference of cycle condition is large indicates that the initial state temperature of vehicle thermal management has a greater impact on the application efficiency of energy management.