Abstract: The interaction between the underbody flow of a high-speed maglev train and the track structure at 600 km/h results in a non-uniform lift distribution, substantially complicating suspension control and introducing safety risks. To address this issue, this study investigates a three-car formation using a high-precision numerical approach based on the compressible SST k-ω IDDES turbulence model. The effects of slotted track width (320–1280 mm) on aerodynamic characteristics and flow structures are systematically examined, with wind tunnel tests validating the numerical model. Results show that slotted track width critically governs the pressure distribution, velocity field, and aerodynamic forces on the train underside. As slot width increases, the positive pressure zone beneath the leading car contracts, reducing its lift; conversely, the negative pressure zone under the trailing car weakens while the positive pressure region near the skid's windward side expands and intensifies, increasing trailing car lift. Flow field analysis indicates that the slot-induced modifications to the train-track gap flow enhance the airflow rate and high-speed flow coverage, driving changes in pressure distribution and aerodynamic forces. Comprehensive assessment reveals that at a slot width of 960 mm, total aerodynamic drag is minimized, leading to a 10.9% reduction (22.26 kN) in leading car lift and a 15.8% increase (32.26 kN) in trailing car lift compared to the non-slotted track, thereby significantly reducing the lift difference between cars and achieving optimal aerodynamic balance. This study provides a theoretical foundation for enhancing the stability and safety of high-speed maglev trains via passive flow control through slotted track design.