Abstract The univariate sweeping tests for fuel injection pressure, injection timing and exhaust gas recirculation (EGR) rate were conducted on a three-cylinder gasoline extended range Atkinson cycle engine (ACE). The effects of above parameters on combustion, emission and performance of ACE were studied and some useful conclusions were obtained. In general, injection pressure has little effect on combustion and engine performance except at the injection advance of 280 deg, while its effect on emission is obvious. With injection pressure rising, NOx first increases and then decreases, while CO follows a reverse trend. Compared with injection pressure, injection timing has more significant effects. As injection timing is advanced, the max combustion pressure first increases and then decreases and the peaks appear around 300deg and 320deg. The lower EGR rate reduces BSFC and NOx with little influence on other emissions. At the EGR rate of 7%, NOx decreases significantly (up to 57.5%), CO, particle number (PN) and particle density are almost unchanged, and BSFC decreases by 4 g/(kW·h) at most. As EGR rate increases to 11%, only NOx further decreases, while other emissions become worse. Thus, a lower EGR rate (e.g., 7%) combining with reasonable injection advance (300deg) is suggested to improve ACE performance.