Abstract: The performances of spark-ignition biogas engine were studied by using the biogas as the fuel, which was produced from the controllable thermal cracking of agricultural and forestry residues with the procedures of removing dust and tar as well as cooling. The speed fluctuation, biogas consumption rate and harmful exhaust of the spark-ignition biogas engine were tested, and the output power, economic performance, running stability and exhaust characteristics were analyzed. The experimental data showed that the engine could run stably at the idle speed, the biogas consumption rate was low and flat in a large range of power, the speed fluctuation within the full load could meet the demands of national electric network, the exhaust amounts of HC, CO and NOx were low, and no tar deposition arose in the process of combustion. So the conclusion was drawn that the biogas produced from the controllable thermal cracking of the agricultural and forestry residues could be used as the alternative fuel of the spark-ignition engine.