To study the stability margin sensitivity to the parameters of the geared rotor system is prerequisite to carry on structure optimization design and vibration control. The global dynamic equations of the geared two rotor system are set up through the coupled matrix of the spiral bevel gear pairs, and the stability margin is obtained by analyzing the global dynamic equations. To enhance the damping of the bearings and to enhance the module and mesh damping of the gear pairs can improve the stability margin of the geared rotor system. The method for the stability margin sensitivity analysis of the geared multi-rotor system is feasible. The conclusions from the numerical example are useful to improve the stability margin of the geared multi-rotor systems.