In this study, to overcome the inherent problem caused by simulating infinite rail using finite rail, a method that combines flexible rail embedded in SIMPACK and a flexible track board imported from ANSYS on a SIMPACK platform is first proposed, by which vehicle-flexible track coupling is effectively realized. The method takes into account the simulation precision and computational efficiency. Using the proposed method, and comprehensively considering wind load, track irregularity, and minor track elasticity, the dynamic characteristics of high-speed train are solved conveniently and quickly. They are simulated under the conditions close to the objective reality. On this basis, the influences of many factors on the vibration characteristics of the train are analyzed, which include car body state, track state, mode numbers of the car body, wind load, track irregularity, and vehicle speed. In addition, the simulation results are basically consistent with the test results. This work lays a solid foundation for subsequent research on noise, fatigue, and the reliability of the train.