• A biomimetic fishtail effectively suppresses alternating vortex shedding in the wake of high-speed trains, aligning drag fluctuation with fishtail oscillation.
• The optimal configuration (1850 mm Eel fishtail, λ=1, T=8 s) achieves drag reduction rates of 39.12% for the tail car and 26.00% for the entire train.
• Fishtail length, oscillation mode, and frequency significantly influence wake flow and aerodynamic drag, highlighting the importance of parameter optimization.
• These findings provide a theoretical basis for designing low-resistance railway trains, contributing to sustainable and energy-efficient rail transit.