To study the operation safety of heavy-load locomotive under effect of longitudinal force, by comparing the dynamic performance of different line conditions, different coupling force state and different coupler rotation angle, the relationship of operation safety and coupler force state, and line conditions and coupler rotation angle under longitudinal force were obtained. The result showed that the safety index was increasing with the line curvature; the safety index increased with coupler pressing force when the locomotive runs on curve line; locomotive coupler would appear horizontal deflection, and coupler rotation angle increases both on straight and curve line with the coupler pressing force. The suggestion were provided when heary-load locomotive throughing a small radius curre under longitudinal force that the locomotive regeneration should be reasonably controlled to avoid the risk of failure of locomotive coupler stability.