The composition of fuel gas derived from biomass gasification has significant impact on the exhaust temperature, peak fire pressure, effective thermal efficiency and flue gas emission of internal combustion engine. The combustion rate of each gas component and the flame-retardant composition in the fuel gas influence the combustion of mixed gas in the cylinder, and simultaneously influence the gas emission. The results show that the low gas heating value and slow gas combustion velocity in the cylinder are main reasons of higher exhaust temperature, lower peak fire pressure and higher energy consumption. The analysis of the fuel gas emission test shows that complete combustion of the mixed gas can reduce the emission of smoke, CO and HC, NOx emission can be decreased by reduction of combustion temperature.。