The condition of dynamic balance, the formula of dynamic non balance angle and the synthesis of dynamic balance peculiarity of two series bodies were presented.

The vibrating spectrum analysis was done to centrifugal multi-level impeller blower, and found that the impeller has dynamic unbalance, so that the vibration of blower is to exceed the standard.

Two kinds of unbalances including static unbalance and dynamic unbalance are imposed on the rotor system. The gyroscopic effect and the gravity are included.