Abstract: The performance of the power, economy and emission of biogas engine were studied by experiment of large bore non-pressurized spark-ignition biogas engine using thermal cracking low heat value biogas as fuel. The effects of different operation parameters and different thermal cracking biogas on the power and harmful emissions of the engine were measured. The experimental data showed that the engine run stably in whole operating range, the combustion speed was low and the combustion was the best at BTDC32°CA ignition advance angle. The emission performance of the engine was better. The NO emissions increased with load increase, while the emissions of HC and CO decreased with the load increase. The NO emissions increased with the increase of calorific value of the cracking gas. The results indicate that the stable running and better economy and emission performances can be realized by using thermal cracking low heat value biogas as fuel of large bore engines.