Abstract: Aiming at the failure against structural damage in the exposed section of adiabatic diffuser during ground hot-firing test of a heavy-lift carrier rocket, the failure mode analysis was carried out, based on the modal results and the measured data of power spectral density also, the dynamics simulation was calculated. The simulation results show that the adiabatic diffuser at the junction with the tail of the nozzle shell generates a higher alternating stress under the action of high vibration load, with the continuous high-temperature, high-pressure and high-speed gas flow and particle scouring of the rocket motor, the material performance of the adiabatic expansion section is reduced, the inner surface of the high-stress site begins to exhibit abnormal phenomena such as carbon cloth shedding, and the wall thickness continues to decrease, which eventually leads to cracking at this site and triggers the disintegration of the adiabatic diffuser. According to the above fault location, a reinforcement scheme for extending the nozzle shell is proposed, which increases the structural integrity maintenance ability of the adiabatic diffuser under high vibration load environment, and successfully passes the verification test of the ground hot-firing test, indicating that the improvement scheme is reasonable, the measures are effective.