Abstract: Aiming at the speed enhancement and remoulding engineering of Jingqin Railway Line, a dynamic computer simulation of the vehicle-subgrade system is performed. Under various speed and strengthening conditions of subgrade, the safety, comfort index of the vehicle and the main dynamic characters of track and subrade are analyzed. Comments and advice are given. The suitability of the current subgrade to increasing speed to 200km/h and the feasibility of strengthening design are addressed. The results of the calculation are compared with the test results of vehicle. The reliability of the simulation analysis is verified by the test results.