Abstract: The rotor of helium circulator in high temperature gas-cooled reactor is supported by magnetic bearing. The auxiliary bearing of the magnetic bearing is used to support and protect the rotor when the magnetic bearing loses the power. In this helium circulator, the auxiliary bearing is the sliding bearing which is easy to be broken by the frictional heat when the rotor drops down at the full speed. In this paper, a pneumatic protection system of the auxiliary bearing was designed, and it could reduce the impact when the rotor dropped and protect the auxiliary bearing from more damage. An experiment platform was designed to validate the reliability of the protection system. For simulating the impact of the auxiliary bearing when the rotor dropped, a magnetic load simulator was designed, which can exert axial load to the motor directly by electromagnetic force through a similar technology to the magnetic bearing. The design axial load of the magnetic load simulator is 110 kN with a clearance of 1 mm. By analyzing and calculating the parameter of the magnetic load simulator, the result shows that the magnetic load simulator can meet the loading requirement of this test.