To provide a theoretical basis for operational safety risk assessment of heavy-haul trains, this study investigates common power-loss faults in the braking system through multi-condition simulations based on a longitudinally dynamic model validated by experiments. Using nine typical fault modes and seven typical line segments derived from actual operational scenarios, the maximum tensile compressive coupler forces and longitudinal acceleration responses under fault conditions were analyzed. The simulation results from the established model closely align with experimental data, demonstrating the model’s reliability. The findings indicate that the level of longitudinal impulse is collectively determined by the fault type, dynamic state, and line gradient. Specifically, power loss in the non-operating section of the leading locomotive under traction (Fault?1) generated the maximum tensile coupler force of 1,370?kN on a 3‰ upgrade. Power loss in the operating section of the trailing locomotive (Fault?3) produced the highest peak longitudinal acceleration of 7.59?m/s2 on a 4‰ upgrade. Power loss in the non-operating section of the trailing locomotive under combined braking and traction conditions (Fault?7) resulted in the maximum compressive coupler force, exceeding 1,000?kN, on a descending section with a gradient transition from -12‰ to -8‰. Moreover, faults occurring at gradient transition zones further intensify longitudinal impulses and elevate operational risks. This research provides theoretical and data-driven support for the development of fault emergency strategies and operational optimization.