When a space vehicle reenters into the Earth’s atmosphere, it receives severe aerodynamic heating. In order to protect the space vehicle from such heating, an ablation method is used widely. Carbon-based heat-resistant materials are mainly used for ablation materials, and silicon-based heat-resistant material are also expected. In our laboratory, ablation experiments of silicon carbide as a silicon-based heat-resistant material have been performed systematically in air plasma freejets. In this study, an automatic position control system which changes the heating rate conditions during the ablation experiment was applied and the weight losses were estimated experimentally. As the results, the weight loss rates of the test piece were 2.71 kg/m2 · s at 4.2 MW/m2 and 4.84 kg/m2 · s at 5.2 MW/m2.