Abstract: In order to study the combustion characteristic and its effect factors and to predict performance of LPG (liquefied petroleum gas) engine, simulations of working processes of GY6 LPG engine and gasoline engine are carried out. Indicator diagram are measured by experiments. All results computed are compared with the experimental results and the feasibility of the combustion model is verified. Based on the analysis of turbulent vortex structure and turbulence characteristics in cylinder of S I engine, two-zone quasi-dimentional model for S I engine is set up in this article, simulation of combustion process of GY6 gasoline engine is carried out by using gasoline and LPG and the calculation of combustion process is realized through the foundation of corresponding sub-models and equations; the computed results are proved reasonable and the model set up in the research of prediction of S I engine performance is feasible.