Abstract: The streamlined nose length plays a crucial role in determining the aerodynamic performance of high-speed trains. An appropriate streamlined nose length can not only effectively reduce the magnitude of aerodynamic drag and lift forces, but it can also improve the performance of the high-speed train in tunnel passing and crosswind circumstances. In this study, a numerical simulation of the aerodynamic performance of high-speed trains at a speed of 400 km/h, with varying streamlined nose lengths, is conducted using the k-ω Shear Stress Transport turbulence model. The different streamlined nose lengths include 6, 7, 8, 9, 9.8, 12, 15, and 18 meters. In order to validate the accuracy of the numerical simulation, its results are compared with wind tunnel test data obtained from the literature. Numerical simulation is carried out using compressible and incompressible gases to determine the effect of gas compressibility on results. The impact of streamlined nose length on the aerodynamic performance of the trains is analyzed in terms of aerodynamic forces, velocity, and pressure distributions. In comparison to the original train, the train with a 6 m streamlined nose length experienced a 10.8% increase in overall aerodynamic resistance. Additionally, the lift forces on the head car and tail car increased by 35.7% and 75.5% respectively. On the other hand, the train with an 18 m streamlined nose length exhibited a 16.5% decrease in aerodynamic drag. Furthermore, the lift forces on the head car and tail car decreased by 21.9% and 49.7% respectively. The aerodynamic drag force of the entire train varies linearly with the streamlined nose length, while the aerodynamic lift of the tail car follows a quadratic function in relation to the streamlined nose length.