Abstract: Based on the gyro approximate theory and the relative motion dynamics theory, two topics are discussed first, they are: (1) precession of the Two-degree freedom gyro, (2) rotation of rotor around the single-degree freedom axis when a gyro axis is forced to rotate around an axis which lacks degree of freedom in a single-degree freedom gyro. And then the difference betWeen the principle which leads to these two kinds of gyro dynamics property and the law of motion is pointed out.