The combustion and emissions of a gasoline direct injection (GDI) engine were studied during constant-speed and increasing-torque conditions by transient engine control and measuring system. The effects of transient throttle switching duration and amplitude were investigated. The close-loop λ proportion and integral(PI) control for fuel injection strategy and the throttle overshoot strategy were tried to show their potentials to improve the transient combustion and emissions. The results revealed there were different degrees of time lags for engine working parameters compared with throttle opening, and the longer switching duration would shorten the lags. The stabilities of the working parameters became worse when the switching amplitude was larger. The response characteristic of intake air was thought to be the major factor that affected the transient combustion and emissions. In this paper, the combination of P=0.08/I=0.5 was the best to shorten the time lag with throttle opening and reduce the particulate number and hydrocarbon (HC) emissions. Compared with PI optimization strategy, the throttle overshoot strategy could be more efficient to shorten the intake response delay, making more fully combustion and reducing particulate number and HC emissions in the transient conditions.