A physiochemical model of the self-deflagration of pure single crystal of ammonium perchlorate (AP) has been developed in this paper. The values of the self-deflagrating rate. pressure exponent and burning surface temperature at the pressures between 10 and 800 atm are calculated. The resucts are in good agreement with the experimental data made by Boggs.^[2] The calculations are based apon the assumptions that the decomposition of crgstal AP follows two competitive process. At low pressures，AP melts at first，decomposes and then the products react each other in the condensed phase accompanying with the generation of heat. The exothermic reaction in the condensed phase is the main heat source of Ap def1agration at low pressuress. And at the high pressares，the beat transferred from the gas phase to the burning surface increases rapidly，forming the direct decomposition and vaporization of crystal Ap. The regularity of burning rate changing with the pressure obtaind by Boggs' experiments can be clearly illustrated from these assumptions and calculations. This paper also uses a kind of new chemical reaction rate expression dT/dt (T is "temperature") to describe the Ap deflagration and presents the calculation method. This new expression facilitates the calculation of gas phase temperature gradient and makes the theoretical modeling succeed.