A modeling method was presented to analyze the vibration of a multi-rotor system.The multi-rotor system was divided into single-rotor systems at the coupled parts.The coupled forces were regarded as the external exciting forces for each single-rotor system.The vibration equations of the single-rotor system were derived from the lumped mass method and the vibration equations of each node.The coupled matrixes of the multi-rotor system were deduced from the expression of the coupled forces.The global vibration equations of the multi-rotor system were established using the coupled matrixes.The nature frequencies

critical speeds

frequency amplitude diagram and whirling orbit etc.

were obtained by analyzing the global vibration equations of the whole systems.Finally

the feasibility and the reliability of the substructure coupled matrix method for vibration analysis of multi-rotor system were proved though two numerical examples.