Abstract: In order to provide optimization suggestions for the thermal design study on the 20 cm diameter LIPS-200 ion thruster with ring-cusp magnetic field, steady-state and transient thermal analysis are performed utilizing the calculation results with the internal discharge energy deposition mathematical model of the LIPS-200 ion thruster. Thermal balance experiments are conducted to validate these results. The results indicate that the internal magnet is the key factor influencing the thermal design of the thruster as the thruster is in steady operation, while increasing the surface emissivity of the internal and external components of the thruster can reduce the temperature of the internal components effectively, roughly by the order of 50~60 ℃. The thermal balance experiment results is in agreement with the theoretical analysis results.