Abstract: The effect of octane number on engine power output, fuel consumption, and exhaust emissions were investigated for a turbo-charged gasoline direct injection(T-GDI) engine through bench test. The test results show that the power performance of the engine fueled with high octane gasoline could be improved, and the IMEP of the engine fuelled with 97# gasoline was up to 4.07% higher than that of 97# gasoline at the external characteristic of 2000r/min. The fuel consumption of the engine fuelled with 97# gasoline was lower than that of 95# under test conditions, and the decrease got bigger at the medium load, the maximum decrease was up to 2.8% when the speed reached 2000r/min and the BMEP reached 0.9MPa. High octane number gasoline was adverse to reduce THC and CO and NOx emission. Compared with 95# gasoline, CO and THC emissions were increased significantly at high load under the test speed. NOx emissions were influenced by speed and load, it increased obviously at higher speed with load increased.