In order to improve the accuracy of the numerical simulation of aircraft cabin fire, the full-scale A320 cabin fire model was established by using FDS (fire dynamic simulation), a 3D fire dynamics simulation software, and the influence of the change of the computational domain caused by the pyrolysis of combustible materials on the temperature characteristics was analyzed. The results show that considering the pyrolysis change of combustibles during the combustion process, the cabin heat release rate and the temperature field will be changed, and the maximum difference can reach 328 ℃. When the calculation area is extended to 2 m, the correlation values between the cabin temperature field and the temperature field at the fire source increase to 0.975 0 and 0.964 2, respectively, in order to minimize the calculation time under the premise of ensuring the accuracy of numerical simulation, it is recommended to extend the calculation area outward by 2 m.