Abstract: During the launch and recovery phase of the reusable rockets, the fuel-rich exhaust gas in their tail flames will undergo afterburning with the oxygen in the air. To rapidly analyze the impact of afterburning on the thermal environment of the rocket body, a chemical kinetic model suitable for describing the afterburning of liquid oxygen (LOX)/methane rocket tail flames was established. The DRGPFA method was used to eliminate redundant components and reactions from the Gri-Mech 3.0 mechanism model, and the calculated results were verified using experimental data from the literature. The effects of environmental parameters (pressure and temperature) on the combustion process were analyzed. Subsequently, temperature sensitivity analysis was carried out to obtain simplified reaction mechanism models with ten components and fourtenn steps, and nine components and seven steps, respectively. The results demonstrate that environmental parameters have a significant influence on the combustion process, and the calculated values from the various simplified models exhibit consistent trends across different reactor configurations. The simplified mechanism model established in this study can effectively predict the temperature field, free radical distribution, and heat release characteristics in the secondary combustion region, providing a theoretical and computational tool for thermal protection design of reusable rockets.