Elastic ring squeeze film damper (ERSFD) has a good supporting and vibration reduction effect. However, due to its complex structure and flow field coupling behavior, existing physical models are difficult to fully demonstrate the mechanical characteristics of ERSFD. To further explore the mechanical mechanism of ERSFD, this paper analyzes the interaction between elastic ring and oil film with the aid of finite element simulation platform and bidirectional fluidstructure coupling calculation method, and obtains the distribution law of oil film pressure in the ERSFD. On this basis, the mapping relationship between the equivalent stiffness and equivalent damping of ERSFD and the disturbance displacement of the rotor journal is further fitted by using the least square method. Then the equivalent model is further introduced into the dynamic model of the flexible rotor system. The vibration response of flexible rotor system supported by ERSFD is studied by numerical calculation, and the response bifurcation diagram and whirling orbit of the rotor system under different speeds are conducted. At the same time, through comparative analysis, the rich nonlinear dynamic behaviors of rotor system induced by ERSFD are further revealed, which is helpful to understand the supporting characteristics of ERSFD.