To study the combustion performance of self-extinguishing solid propellants and the pressurization-induced extinguishing mechanism， HTPB/AOT/AP self-extinguished solid propellants were prepared by using sodium dioctyl sulfosuccinate （AOT） as extinguishing agent. Experimental characterizations of burning rate， combustion wave structure， flame morphology and flame quenching burning surface topography of the propellants were carried out. Results show that AOT reduces the pressure exponent of propellant below 10 MPa from 0.37 to -1.36， and the burning rate decreases from 5.9 mm·s^-1 to 2.9 mm·s^-1 as the pressure approaches the critical extinguished pressure. AOT causes the propellant to self-extinguish when the pressure increases to 10 MPa， with unsustainable combustion observed at higher pressures. As the pressure approaches the critical extinction pressure， a molten layer with a thickness of 230 μm covers the burning surface of propellant， reducing the burning surface temperature from 865 K to 420 K and the gaseous phase temperature gradient from 74.9 K·μm^-1 to 0.19 K·μm^-1 compared with that of pressure of 2 MPa. The pressurization-induced extinguishing mechanism of self-extinguishing solid propellant is revealed. AOT causes a thicker molten layer to cover the surface of propellant， obstructs the heat feedback from the gaseous flame to the burning surface， reduces the temperature of burning surface and the reaction rate of condensed phase， and ultimately results in extinguishment due to the failure to maintain self-sustained combustion.