Compared with the main trunk line of heavy haul railway, the railway line in mountain area often has a larger slope and contains a large number of small radius curves, which makes the safety of train operation more threatened. Based on the actual engineering demand of a mountain railway planning to run 5000 tons heavy duty train to increase the railway capacity, a field test was carried out to test the data of wheel-rail force when train passed through. Through mathematical statistical analysis, the variation rule of each dynamic index and the running safety of each locomotive and vehicle under different running speed and curve radius are analyzed. The result of research shows that the dynamic indexes of locomotive and vehicle under different working conditions are all within the safety limit, among which the wheel load reduction rate and the vertical force of wheel and rail have a large margin compared with the safety limit, while the lateral force of wheel and the derailment coefficient have a relatively small safety margin, especially the derailment coefficient. The research results can provide data support for the smooth operation of 5000t heavy-haul train in the mountainous area.