When the nozzle is working, there is large amount of hot gas at the interface of the carbon-carbon(C/C) exit-cone because of the pyrolysis of insulator. The hot gas may cause high pressure which may impact the reliability of the joint structure. So the high temperature and pressure measurement were developed to measure the temperature and pressure at the interface of the C/C exit-cone and the insulator. The result shows that the hot gas makes pressure at the interface of the C/C exit-cone. Different exit-cone materials, pressures are different. The higher the density of the C/C material, the higher is the pressure. The effect of the pyrolysis hot gas to the reliability of the joint structure was also analyzed.