Single freedom system frequency has very important significance in the structural dynamics calculation. The current method of calculating freedom system frequency is relatively single, and the calculating method of multi-particle freedom system natural frequency is more cumbersome, in particular, the current solving method for the natural vibration frequency of multi-particle inertia noncollinear generalized freedom system can not be unified with the calculation formula of single freedom system natural frequency. This paper solves this with inertial moment method, being able to unify it with the calculation formula of single freedom system natural frequency. The calculation examples show that this solving method is relatively convenient, easy to grasp, and of the spreading and application value.