To improve the bottom flow field structure and further reduce the aerodynamic drag of the high-speed train， based on the idea of bottom flow control， a triangular cross-sectional deflector located before and after the bogie cabins on the train bottom is designed， and its aerodynamic drag reduction characteristics are studied. Taking the open line running high-speed train with three coach formation CRH380B at the speed of 300 km/h as the research subject， and using the Realizable k-ε turbulence model， four typical deflector installation positions are explored， and the deflector installation position with the best drag reduction effect is selected to investigate the differences of deflector drag reduction characteristics under different combinations of five angles and five heights. The drag changes on the train bodies， bogies， and bogie cabins before and after the installation of the deflectors， the pressure distribution changes， and the flow field structure changes in the bogie area are also compared. The results show that the best drag reduction effect is achieved only when the deflectors are installed in the direction of incoming flow in front of each bogie cabin in both directions. After the installation of the deflectors， the aerodynamic drag on the train bodies and bogie cabins increases， but the drag on the bogies is significantly reduced， the flow velocity and the pressure difference in the bogie areas decreases， and the bottom flow field is significantly improved. At the same time， it is found that the 15° and 100 mm combination of the deflector has the best drag reduction effect， and the drag reduction rate of the three cars reaches 7.08%. The numerical simulation proves that the bottom deflectors can effectively reduce the train running resistance.