Based on the three-dimensional finite element slope dynamic analysis model which is validated through the test data of 1：7 indoor physical model for live tree stump，the attenuation characteristics of additional dynamic stress on live tree stump slopes，the stress response characteristics of taproot and lateral root of live tree stumps，and the influence of live tree stumps on slope stability are studied. The dynamic stability mechanism of live tree stump slope is explored. The research conclusion is as follows. The peak value of vertical dynamic soil pressure calculated by the three-dimensional finite element dynamic analysis model is close to the measured results of the indoor physical model. The method and calculation results of the three-dimensional finite element dynamic analysis model of the live tree stump slope established through Midas GTS NX are reliable. The peak value of additional dynamic stress on the slope is affected by the superposition effect of train axle load. The higher the train movement speed，the greater the peak value of vertical dynamic stress. The additional dynamic stress in the ballast layer is the largest，it rapidly decays and diffuses downwards showing a semicircular arc shape. Only small dynamic stresses are transmitted to the two rows of live trees on the upper slope. The degree to which the shear resistance of the taproot of live tree stumps varies at different positions，and the taproot at the foot of the slope is subjected to greater shear stress compared to the taproot at the shoulder of the slope. The taproot is similar to the anti-slide pile to exert its shear resistance ability. The side roots of live tree stumps growing inside the slope are similar to anchor rods，while the side roots growing outside the slope are similar to supports，and they form an anchor-support effect that synergizes with the main root to play a sliding resistance role. The existence of live tree stumps leads to a redistribution of stress in soil，and the shear stress concentration near the live tree stumps. The live tree stumps hinder the transmission of shear stress in soil，inhibit the connectivity of plastic zones，and improve slope stability. The degree of influence on the horizontal dynamic displacement of the slope is related to its distance to the location of the dynamic load，and the closer the distance，the greater the impact. The live tree stumps can reduce the horizontal dynamic displacement at various points on the slope，but the reduction at the foot of the slope is the greatest. The live tree stumps can significantly improve the stability of slopes under train power，and their slope safety factor can be increased by 15%~20%. The potential sliding surface of the live tree stump slope presents a circular arc shape，and the live tree stump moves the plastic zone towards the deep soil layer，thereby improving the stability of the slope. The research results can provide certain guidance for the application of live tree stumps in roadbed slopes.