Abstract: Longitudinal dynamic analysis for 20-groupage, 18t-axle-load high-speed wagons under the operation of service braking and emergency braking were investigated using longitudinal dynamics analysis system, which was based on air brake system emulation. According to the simulation results, the longitudinal impulsion was differentiated into two parts, which were “extrusion coupler force” and “impact coupler force”. Some advises were also put forward to reduce the longitudinal impulsion.