In order to explore the dynamic features of subgrade under the dynamic load of heavy-duty train，based on the background of cement-stabilized expansive soil subgrade in San-Jing（Sanmenxia-Jingmen）test section of Hao-Ji（Hollerbaoji-Ji'an） heavy-haul railway，field vibration tests no less than 4 million vibration times are carried out. Using large-scale excitation equipment and counterweight combination，the effect of heavy-duty train with axle load of 25-30 t at 120 km/h is simulated and compared with the test results of reserved passenger train with axle load of 21 t at 120-200 km/h. The results show that the sensitivity of dynamic stress affected by axle load is greater than driving speed，and the amplitude range of dynamic stress on the subgrade surface under axle load of 25-30 t is about 1.2-1.4 times of that of 21 t passenger train；the dynamic stress and acceleration attenuation trend along the subgrade depth are consistent，and the maximum range attenuation can reach 40% and 80% respectively in the surface layer and bottom layer of subgrade bed，and the dynamic influence depth is slightly greater than the design of subgrade bed thickness；the cumulative deformation of the subgrade surface is "fast-slow-stable"，which is controlled within 4 mm when it is stable，among which the first 1.5 million times account for 90%；combined with the test results，it is estimated that the dynamic stability of 3%-5% modified expansive soil used as the bottom layer of subgrade bed and the embankment below meets the requirements.The research results can provide the theoretical reference for the exploration of dynamic level and structural design of heavyhaul railway bed.