Abstract: The investigation and analysis of power performance, economic performance and idle emission axe carried out on a type 1-4 spark ignition engine burning two different ratio of mixed oils which are made up of No.93 gasoline, vegetable oil, water and emulsion. The results indicate that (1) When burning mixed oil, the CO and HC emission concentration clearly decreases compared with burning gasoline at idle running condition. (2) When burning mixed oil, the oil consumption rate decreases compared with burning gasoline at full load running condition of engine at the speed of less than about 2 500 r / mm; At full load running condition of engine at the speed of larger than 2 500 r / mm, the oil consumption rate increases. (3) When burning No.1 mixed oil, the maximum torque and power of the engine respectively decrease by 6% and 7% compared with burning gasoline at full load running and the engine torque is rapidly decreasing with engine speed increasing.