Abstract: To address the operational safety issues of the mid-locomotive in a 20,000-ton heavy-duty combined train, a dynamic model of the heavy-duty combined train in a "1+1" formation is established based on the structural characteristics of the 102-type locomotive coupler. The study explores the influence patterns of the coupler's free angle on the wheel-rail dynamic interaction. Additionally, considering the lateral force limit of the locomotive wheelset, an analysis is conducted to further examine the compressive coupler capacity of the locomotive under different track conditions. The computational results reveal that, under the longitudinal coupler force in the 20,000-ton heavy-duty combined train, the size of the coupler's free angle significantly affects the safety indicators of the train's operation. Various safety indicators of the train increase significantly with the increase in the coupler's free angle. Specifically, under straight-line braking conditions, when the locomotive coupler's free angle reaches 8°, coupler forces exceeding 800 kN result in the lateral force of the wheelset exceeding the limit. In the case of braking on a small-radius curve with a radius of 300 m and a coupler free angle of 7°, a coupler force of 600 kN leads to the locomotive's wheelset lateral force exceeding the limit. Therefore, controlling the coupler's free angle reasonably and reducing the longitudinal impulse during train operation is of significant importance for ensuring the safe operation of the train.