Increase of axle load and wagon numbers of heavy haul train would generate larger longitudinal train impulse in the condition of shunting impact, and it would result in some dangerous problems. On the basis of draft gear dynamic modification model, the vehicle impact equation and vehicle-coupler-vehicle series model, the effect of different braking conditions and combinations of draft gears of different resistance characteristics on longitudinal impulse characteristics were studied. The results showed that the draft gear dynamic modification model could actually reflect the characteristic of draft gear in shunting impact, and the coupler force variation in brake condition; the vehicle-coupler-vehicle series model could simulate the impact of locomotive and freight vehicles equipped with different drafts gears well, and it had some guidance for selecting suitable draft gear.