Experiments were separately carried out on Liquefied Petroleum Gas (LPG) and gasoline as fuel for a spark ignition (SI) engine. According to the indicator diagram and the calculation of corresponding heat release, combustion characteristics of the two fuels were analyzed. The results showed that using LPG would lead to 7.64% power reduction and a little peak pressure reduction when the structures and ignition advance angle of the engine were remained. At rated speed and full load, the power of engine fueled with gasoline reaches the maximum when the excess air ratio is 0.90 and 0.76 fueled with LPG; when comparing the maximum power and specific heat consumption at different excess air ratios, we can see that the change of excess air ratio has a greater effect on the engine fueled with gasoline than that fueled with LPG; the specific heat consumption of both fuels decrease with the increase of load. Besides, under the same Фa, LPG has a shorter combustion delay period, faster combustion speed and shorter combustion period than gasoline.