The model of a 1.5T gasoline direct injection engine was built with 3D CFD software and the laws of incylinder flow field, fuel atomization and combustion process were compared and analyzed at full load of 2 000 r/min based on the asynchronous exhaust valve timing. The results showed that the flow field in the cylinder was different from that of the original engine when the nonsynchronized exhaust valve timing strategy was adopted. The turbulent kinetic energy exhibited a characteristic of three peaks and its average value was greater than that of the original engine which had the greatest change when the exhaust valve 1 opened at the advance angle of 20°CA.Compared with the original engine, the average flow velocity of incylinder mixture increased, the fuel evaporation rate improved, the incylinder mixture on the top dead center became more uniform, but the residual gas increased. In addition, the incylinder combustion accelerated and the maximum pressure increased by 0.3 MPa.The in-cylinder temperature decreased and hence NO_x emission reduced, but CO emission kept the same. However, delaying the exhaust valve 1 by 20°CA would make no difference. Accordingly, advancing the exhaust valve 1 by 20°CA could improve the power and emission characteristics of the original engine.