Accurate heat flux measurement is essential for developing hypersonic vehicles and their thermal protection systems. The intense aerodynamic heating generated during high-speed flight of aerospace vehicles is primarily dominated by convective heat transfer. However, existing heat flux gauges struggle to accurately measure surface thermal loads under extreme high-temperature and high-speed conditions, resulting in low measurement accuracy and significantly constraining the performance evaluation of thermal protection systems and material development. To address the lack of reliable calibration methods for heat flux sensors under high-temperature and high-speed conditions, this study introduces a dual-plate transient calibration method. This method adopts a highly accurate thin-film platinum resistance sensor as a reference, installs a Gardon gauge to be calibrated with the sensor together on a displacement ejection mechanism, and simulates the high-speed flight scenario of the aircraft in the wind tunnel to achieve the calibration to the Gardon heat flux gauge under airflow conditions. Calibration experiments were conducted at a flight Mach number of 0.3 and temperatures from 100 °C to 300 °C for the developed convective heat flux measurement device. The results demonstrate that the relative expanded uncertainty is 4.2% (k = 2), and this method can effectively obtain the convective heat flux sensitivity coefficient of the Gardon heat flux meter. The dual plate transient calibration method proposed in this paper provides new ideas and approaches for high-temperature and high-speed convective heat flux calibration, significantly improving the reliability of convective heat flux measurement data and providing strong technical support for the development of hypersonic aircraft and accurate measurement of thermal loads in thermal protection systems.