Abstract The thermodynamic behaviors analysis for the transient flow of a compressible gas in a duct after an accidental rupture is undertaken based on the numerical simulation, which is performed by solving the coupled conservation equations, momentum equations and energy equations of an axisymmetric, transient, viscous flow. Applied in high temperature and high pressure atmosphere, super high temperature gas-carrying duct is constructed in structure as: thermal insulating media is installed between the liner tube and the outer wall of the hot gas duct. This structure is widely used in engineering such as the pipeline of the nuclear reactor, oil transportation and aerospace engineering. The pressure and the temperature, and their corresponding differences in insulating media and depressurization channel are calculated numerically. The results show that the depressurization rates in the insulting media and depressurization channel are much lower than that in the hot gas duct, and due to the insulting media, the max pressure differences vary with different amplitudes of depressurization. Compared the results with available experimental and numerical data conducted by Weber, they share the same trends though there are differences between the simulation and the experimental results, and the comparisons validate the effectiveness of the model and method.