Abstract: In high-speed flight, the aircraft can use its own propellant to cool through the micro-hole jet to achieve active thermal protection. The interaction between the compressible external flow and micro-jets under high-temperature non-equilibrium conditions involves complex processes of jet extrusion, mixing, and reactions. This study aims to elucidate the dominant mechanisms and influencing factors of propellant micro-jet cooling. We establish a viscous wall boundary model for micro-jets and conduct numerical simulations of high-temperature non-equilibrium flow fields under micro-jet influence. The simulations reveal the impact mechanisms of micro-jets on chemical reaction boundary layers, wall heterogeneous catalysis, and aerodynamic heating characteristics. The findings indicate that propellant micro-jet cooling under high-temperature non-equilibrium flow conditions is dominated by two key processes: boundary layer crowding and heterogeneous catalytic weakening. Specifically, the low-temperature micro-jet ejection crowds the boundary layer, altering its profile and reducing the temperature gradient near the wall, thus decreasing wall-normal heat conduction and achieving cooling. Additionally, the crowding-out effect of the low-temperature micro-jet promotes the outward displacement of near-wall O atoms, weakening the oxygen catalytic effect and reducing catalytic heat. Further parametric study shows that when the mass flow rate is constant, the heat reduction rate and cooling range decrease with the increase of jet hole size. When the area of the jet hole is constant, the micro-jet velocity is increased, and the heat reduction rate and cooling range are increased. When the mass flow rate is constant and the hole spacing is reduced, the peak value of the spanwise average heat reduction rate decreases, but the cooling range downstream of the hole increases, showing a more uniform cooling effect. These findings provide crucial theoretical support and technical guidance for the design and optimization of active thermal protection systems utilizing micro-jet cooling in future high-speed vehicles.