In order to study the longitudinal impulse problem on 20 000 t heavy haul combined train in China, the kinetic model ofcombined train with an example of coal dedicated gondola car of C80 series was established by Matlab/Simulink module. It was mainlyanalyzed that effects of longitudinal impulses under emergency braking conditions for combined train with 1+2+1 type, and types ofcombination, response time of controlled locomotives, structure of vehicles, hook buffer devices, operating conditions and other factors weretaken into the consider. The result indicates that types of combination have a large influence on coupler forces with sizes and distributions.Also shorter response time of controlled locomotives, using traction rod friction rubber buffer can help to reduce coupler forces. Last but notleast, there is the largest coupler force under emergency braking conditions with lower speed and steeper down gradient.