Abstract The large longitudinal impact of heavy-haul trains is the main factor limiting their development, and the asynchronous nature of train-braking systems is the main cause of this longitudinal impact. In this paper, a segmented electro-pneumatic braking solution fully compatible with the existing freight-train braking system in China is proposed to improve the synchrony of train-braking systems. A simulation model for this braking system is developed based on air-flow theory, the 120 distribution valve and electronic control devices. The braking characteristics obtained from simulations are compared to those from the train-brake testing platform, and show high fidelity. On this basis, the effects of the new braking system on the braking capacity and longitudinal impact of a 20 000 t heavy-haul train are analysed by further simulation. The results show that during service brakes, the segmented electro-pneumatic braking system can increase the braking capacity by 4.2–24.7% and reduce the coupler force by 21.6–68.0%. Therefore, it can be seen that the segmented electro-pneumatic braking system is a new type of electro-pneumatic brake that meets the needs of the Chinese railway network. It solves the problem of the longitudinal impact of heavy-haul trains satisfactorily, and its compatibility with the existing braking system (resulting in a reduced modification workload) makes it possible to maintain normal operations on heavy-haul lines while trains undergo modification.