Considering that the superelevation is generally overlarge for curves of Shenshuo Railway, this paper studies the reasonable superelevation modification under mixed traffic of passenger and freight trains, taking curves with 400m radius as example where track damages develop most heavily. Firstly, elaborate heavy haul freight train/ passenger train-track system dynamic models are respectively established, taking into account multiple vehicles. Various components and interactions between components (e.g. contact friction) in the vehicle and coupler buffer device are modeled detailedly. The wheel-rail contact interactions are calculated based on Hertz’s theory and Kalker’s FASTSIM algorithm. The track model is built with the help of field parameter experiments conducted by using self-developed devices. Dynamic characteristics of train-track system under existing superelevation when the freight and passenger trains negotiate curves, as well as the influences of the gradual reduction of superelevation, are investigated systematically based on the established models. According to theoretical simulation results, combined with specifications and actual operation conditions, a modification scheme is put forward, reducing the superelevation by 10mm. In order to examine the effect of this scheme, a curve test section is chosen in Shenshuo Railway, and the superelevation is adjusted accordingly. Dynamic tests are conducted separately before and after the adjustment of superelevation. The comparison of test results shows that the superelevation reduction improves the excess superelevation status to some extent for freight trains negotiating curves. The forces and deformations of inner and outer rails become more balanced, and the global wheel-rail forces and displacements decrease obviously, which can effectively slow down the developments of track damages. This research can effectively solve the problem of heavy damages occurring on inner curved rails for Shenshuo railway. Besides, it also provides a new idea for the rational design of curve superevevation under mixed traffic of freight and passenger trains for heavy haul railway.