The rotor system is an important structure of a centrifuge. The critical speed of the rotor is directly related to the balance of the rotor. In order to study the law of the critical speed of the rotor, a model of the external rotor of the WL-500 centrifuge was established, and the rotor structure was analyzed modally using ansys software to obtain the natural frequency and mode shape to avoid the working speed reaching the critical speed Resonance occurs. By changing the parameters of the rotor system, the influence of the parameters on the critical speed of the centrifuge rotor is studied, and the first and second order speeds of the centrifuge rotor are obtained under different parameters. Based on the obtained critical speed, the influence of external rotor parameters on its critical speed is analyzed. From the analysis data, it can be concluded that the critical speed of the first two stages of the outer rotor of the rotating drum has little effect. The increase of the support span will reduce the critical speed of the rotor. The increase of the aspect ratio will increase the first-order speed and then decrease The second-order critical speed decreases first and then changes little; the increase of the support stiffness will increase the first two-stage speed of the rotor, and the second-order critical speed will change significantly.