Abstract: In order to study the influence of the nozzle’s wall temperature on the plate test in the arc-heated wind tunnel, a thermal insulation semi-elliptical nozzle was designed. A plate test was adopted in the arc-heated wind tunnel with the semi-elliptical nozzle. The bottom of the nozzle wall was connected with the plate model. The flow extended to the surface of the model during the test. The surface heat flux and equilibrium temperature of the model under the conditions of the hot nozzle wall and the cold nozzle wall were measured and analyzed, respectively. The results show that the enthalpy of the nozzle ranged from 1.00 MJ/kg to 2.55 MJ/kg. Compared with the condition of the cold nozzle wall, the surface heat flux of the hot nozzle wall increased by 4.7% to 15.0%, and the equilibrium temperature increased by up to 4.24%. In the thermal protection test, the influence of the nozzle wall temperature on the results of the plate test should be considered, and it is necessary to increase the enthalpy of the flow.