Abstract: Based on finite element theory， a dualrotorbearing system dynamic model was built， which is adopted to analyze the change law of the system critical speed with the bearing stiffness and innerouter rotor speed ratio. The accuracy of the calculated results was verified. The research found that the increase of the supporting bearing stiffness will result in that of the critical speed of system. Not much influence on the critical speed exists when the speed increases to a certain degree. The effects of supporting stiffness on the critical speed are not consistent. Besides， the intermediate bearing affects the critical speed little. When the inner rotor is given a main synchronous antiprecession incentive， the system critical speed will decrease with the increase of the speed ratio. The speed of synchronous positive precession will increase along with the increase of the speed ratio. However， the critical speed will perform a contrary regularity on main synchronous antiprecession incentive given to external rotor.

Key words: dualrotor system, critical speed, finite element model, synchronization motivation, speed ratio