Abstract: Through theoretical analysis and simulation of rubbing of Jeffcott rotor systems, the analytical formulae of the critical rotating speed for rubbing to occur between the rotor and stator was obtained. The influences of the parameters, such as damping, eccentricity and clearance, on the critical speed were discussed. When the ratio between the eccentricity and the clearance is greater than 1, the critical speed decreases with the increase in eccentricity or the decrease in clearance, and increases with the increase in damping. When it is less than 1, the critical speed increases first with the increase in the ratio, decreases after reaching the peak, and decreases with the increase in damping.