In order to improve the dynamic performances of liquefied petroleum gas（LPG） engine and reveal the relationship between the thermal energy and the chemical energy as well as the mechanical energy during combustion,the quasi-dimensional two-zone combustion mechanism is analyzed,with a certain LPG engine as the research objective.Then,a quasi-dimensional two-zone combustion model is put forward,and the curves of crank angle versus cylinder pressure and burnt mixture temperature are obtained by simulation.Finally,the curves are compared with the experimental ones,and the error is found to be only less than 5%.Thus,it is concluded that the proposed combustion model well describes the variations of cylinder pressure and burnt mixture temperature of LPG engine with crank angle.