Abstract: In our report, in order to explore the effects of hydrous ethanol with the volumn of 20% on the combustion characteristics and cyclic variations of gasoline, an experiment was performed on an EFI engine without modification. The results indicated that the maximum in-cylinder pressure of E20 W was 2.18 MPa, 3.91 MPa, and 5.20 MPa, respectively, when the engine was operated at 2000 r·min^-1 with the load of 20 N·m,60 N·m, and full load, respectively. Compared with pure gasoline, under the middle load and low load, the peak pressure was higher, and the pressure rise rate was lower than E0 at the middle and low load, which suggested that E20 W has good knock resistance. Additionally, under the middle load and low load, the coefficient of indicated mean effective pressure and peak pressure of E20 W in consecutive 70 combustion cycles were higher than that of E0, the coefficient of peak pressure increased more obviously. The coefficient of indicated mean effective pressure of E20 W was higher than that of E0 about 0.36% and 0.81%, respectively, the coefficient of peak pressure increased 5.12% and 5.79%, respectively. On the whole, E20 W can be applied in test engine directly with a better anti-knock tendency, however, the driving-stability was worse than that of E0.