With respect to the impact-rub dynamic equations of Jeffcott rotor only with imbalance

the characteristics of every harmonic wave in the spectrum domain are studied according to the 2-dimension holospectrum theory

and an important feature of the impact-rub is obtained.The effects of friction coefficient and rotating velocity on the precession are analysed.It is discovered that the regular forward precession resulting from unbalancing force plays a critical role when the friction coefficient is small

but as the friction coefficient is enlarged

the quasi-periodic precession or instability will appear at certain rotating velocity.