A 10 kg flexible rotor supported by gas bearings test rig was established to conduct the dynamic characteristics experiments with different damping coefficients of “O” rings. The dynamic characteristics of rotor bearing system with acrylonitrile-butadiene “O” rings, fluorine rubber “O” rings, and silicon rubber “O” rings were researched based on the test rig at the same bearing supply pressure, respectively. Translational critical speed, cone dynamic critical speed and the first bending critical speed were below the maximum operating speed of rotor. Vibration amplitudes of the first two critical speeds were similar. The amplitude of working frequency was large and the rotating speed increasing rate decreased at the first bending critical speed. With acrylonitrile-butadiene “O” rings and fluorine rubber “O” rings, the gas film oscillation occurred when the rotating speed was larger than the first bending critical speed and the amplitude increased. It can be concluded from experiments that the dynamic stability of first bending critical speed improved with increasing of O-ring damping. But the low frequency oscillation is more easily to occur and the vibration amplitude increases after the gas whip with larger damping O rings, this is dangerous to the safety of the system.