Abstract: In order to explore the mechanical relationship between roots and soil when trees vibrated under external loads, and then analyze the lodging-resistant mechanism of roots, this study measured the natural frequency of four Chinese white poplars grown in nursery of Beijing Forestry University. Trunk vibration tests were conducted in three different circumstances respectively, which include in-situ growth and root-soil friction and fixed end. The root-soil stiffness connection model, root-soil friction model and fixed end constrained model had been constructed to simulate three circumstances mentioned above. After that the natural frequency of the models had been calculated. Based on a comparison between the simulation values and the experimental values, the effect of interaction between roots and soil on vibration properties of trees had been analyzed. The results show that:(1)the natural frequency of trees in three different root-soil interaction constrained circumstances had obvious difference, the size order was “fixed end>in-situ growth>root-soil friction”.(2)the size order of three finite element models was “fixed end>root-soil stiffness connection>root-soil friction”, it was in accordance with the test result. Root-soil stiffness connection model which was used to simulate trees in-situ was more accurate than other models;(3)Along with the increasing of the external force, the influence of soil on tree vibration properties enhanced gradually.