A dynamic model of dual-rotor was set up.The influence of inter-shaft bearing stiffness and the gyroscopic moments of high and low pressure rotors were considered in this model.The difference of co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response and the influence of speed ratio on co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response were revealed by numerical analysis and experiments.The results show that

gyroscopic moment is a main influential factor to the rotor stiffness of dual-rotor system with inter-shaft bearing

and the changes of stiffness are related to the speed ratio and the relative rotating direction of inner and outer rotors

further causing the change of co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response.Compared with the co-rotating dual-rotor of the same structure with the counter-rotating dual-rotor

the counter-rotating dual-rotor's unbalance response is more obvious than the co-rotating dual-rotor's under the same unbalance mass

and for this reason the unbalance mass of counter-rotating dual-rotor's inner and outer rotors should be controlled more strictly during the dynamic balance.