In order to explore the cumulative plastic strain of weathered soft rock at the base of metro tunnels under long-term cyclic loading of trains, this paper focuses on the weathered argillaceous siltstone at the base of Nanchang Metro and develops laboratory dynamic triaxial tests of working conditions considering dynamic stress ratio, static deviator stress ratio, confining pressure and loading frequency, the dynamic deformation characteristics of saturated weathered argillaceous siltstone under different influential factors are studied. The results show that the cumulative plastic strain of fully weathered argillaceous siltstone and moderately weathered argillaceous siltstone become stable after 1 000 and 100 cycles, respectively, and the critical dynamic stress ratio of fully weathered argillaceous siltstone is between 0.3 and 0.4; compared with different dynamic stress ratios and static deviator stress ratios, confining pressure and frequency have marginal effect on the cumulative strain of the two weathered argillaceous siltstones; by analyzing the test result data, a mathematical model of cumulative plastic strain considering the loading times, dynamic stress ratio and other factors is proposed.