Referring to excessive longitudinal impulse of heavy haul trains in practice when trains make emergency brake at a complex longitudinal section, by using of air braking system and train longitudinal joint simulation system, studied on heavy haul train longitudinal impulse level through the ramp. And the influence of the braking start position、the ramp slope size and train braking velocity on the train longitudinal impulse. The results show: The impulse level is same when heavy haul trains make emergency brake completely at the same ramp uphill or downhill compared with it is at a flat track. It will generate coupler force significantly when heavy haul trains make emergency brake at a complex longitudinal section (such as flat add uphill or downhill add flat ) , For ten thousand tons trains the most dangerous braking position is the fortieth freight car of the train on the ramp. The brake synchronism and the slope of the ramp are the two main factors that influence the longitudinal impulse occurs on grade change point .The ramp slope is smaller, the smaller the train longitudinal impulse level.Increase brake synchronism will reduce longitudinal impulse significantly.