Abstract: Reasonable evaluation of uneven subgrade settlement is key to ensuring the long-term safe operation of high-speed railways and guiding the meticulous maintenance and repair. Traditional roadbed settlement evaluation is mostly based on a single index of settlement amplitude, which lacks the comprehensive consideration of vehicle operating speed and subgrade settlement wavelength. A refined multi-vehicle-ballastless track-subgrade coupled dynamic model was established, and the dynamic response characteristics of vehicles under uneven settlement of subgrade were analyzed, which accounted for the influence of operating speed, settlement wavelength and amplitude on vehicle response. The time-varying rate of settlement index was proposed for the first time in the evaluation of uneven settlement. The results show that the time-varying rate of settlement can integrate the common effects of vehicle operating speed, settlement wavelength and wave amplitude on the dynamic response of high-speed trains. The second-order time-varying rate of settlement has an obvious linear relationship with the wheel-rail vertical force and the safety index of wheel load reduction rate; the first-order time-varying rate of settlement and the vehicle acceleration show obvious linear relationship. Finally, the fitting formulas of wheel load reduction rate, vehicle acceleration and time-varying rate of settlement were put forward respectively. The research results can provide a theoretical reference for the maintenance of high-speed railway lines.