Abstract: In order to solve the bearing misalignment problem of low-pressure rotor system in aero-engines, a dynamic model of flexible rotor system with multi-supports is presented based on analysis of structural and dynamic characteristics. The equations of motion of different structures in aero-engines were derived respectively through Lagrange method. The equations suggest that the dynamic influence of bearing misalignment on multi-supported flexible rotor system varies with different structure types, which will activate the nonlinearity of coupling. An additional 2× excitation force may appear, resulting in other harmonics in the response besides 1× rotating frequency.