Rotor cap for turbomolecular vacuum pump

A rotor cap for a turbo molecular vacuum pump is disclosed. The rotor cap comprises a cover element and a connection element, wherein the side wall and the top surface of the cover element are curved smoothly, and the connection element comprises an extension rod and a hardness and weight adjusting element. The first end of the extension rod is connected to the bottom center of the cover element, the second end of the extension rod is extended in a direction away from the cover element to be adjacent to a rotor shaft, and the hardness and weight adjusting element is connected between the second end of the extension rod and the rotor shaft to reduce the hardness difference between the extension rod and the rotor shaft and to provide a counterweight effect to reduce the rotational vibration of the cover element.