To investigate the effect of post-combustion on the energy addition at tail of base bleed projectile in the transient depressurization process, a mathematical and physical model of the chemical non-equilibrium flow at tail in the transient depressurization process for base bleed equipment was established. Two-dimensional axial symmetric Navier-Stokes equations were solved by idea programming of uniform algorithm using the improved format of convective upwind vector flux splitting format（AUSM+）, the shear stress transport turbulence model SST k-ω and the H₂─CO reaction kinetic mechanism of 12-step reaction of 8 components. The numerical simulation of tail flow field was performed, the change rule of pressure in base bleed combustion chamber in the transient depressurization process with time was obtained. The simulated results were basically in agreement with the experimental ones in the literature. Base this basis, the tail flow field under the condition of with and without post-combustion in the transient depressurization process were numerically predicted, and the change rule of characteristic parameters for the tail flow field of base bleed equipment with time in the transient depressurization process were analyzed. The results show that the post-combustion has a little effect on the tail flow field in the early stage of transient depressurization process, while in the middle and late stage, the post-combustion has a great effect on the tail flow field. At this time, the characteristic parameters of tail flow field more quickly tend to be stable, and the post-combustion makes the temperature of tail flow field increase and the energy addition effect remarkable, the bottom pressure increase, the bottom drag of base bleed projectile decrease significantly and the drag reduction rate increases by 75% compared with that without post-combustion.