The effect of key parameters on the stability of heavy haul locomotive coupler was studied to rapidly estimate the bearing stability of coupler. The structure and longitudinal force principle of the heavy haul locomotive coupler were analyzed, and according to the force analysis and destabilizing condition, the maximum carrying capacity of coupler under the static conditions was calculated based on the force balance method. The results showed that : through unequal radius arc contact point sliding, heavy haul locomotive coupler could achieve reducing the actual transmission line force angle and the lateral force of coupler; heavy haul locomotive coupler required as large as possible locomotive two-lateral suspension stiffness for matching, and enough arc contact friction coefficient.