Abstract: The flight test needs fast response and small transducer for heat flux measurement. The dual-junction thermocouple, which is characterized by fast response, small size and abundant measured information, is one of the best solutions for the temperature and heat flux measurement in the flight test. The principle, structure and measurement method of the dual-junction thermocouple are studied, and dual-junction thermocouples are used in a flight test for the model surface temperature measurement. The model front-surface and back-surface temperatures were measured simultaneously by the dual-junction thermocouples, and it is found that the measured back-surface temperature has a greater error. The response time of the back-surface measurement point is much longer than that of the front-surface measurement point, which is affected by the junction size and the insulating coating between the junction point and the model surface. At present there is still a lack of the corresponding heat flux estimation method for the dual-junction thermocouple.