Abstract: In order to ensure the reliability of the microwave switch channel switching in the temperature range of -40 ℃~+100 ℃, the clearances between rotor and bearing and between bearing and base in the microwave switch are designed and calculated through theoretical analysis and finite element simulation from the theories of thermodynamics and material mechanics. And verification is carried out through tests in this paper. The results show that the bearing clearance simulation of the microwave switch is accurate and reliable. It can effectively prevent the jamming between the bearing and the rotor and between the rotor and the base in the switch, and thus ensure the reliability of switch applications. This simulation method can be applied to the design of bearing clearances for all microwave switches and provide a reference for the design of microwave switches.