Aiming at a 2.0 L naturally-aspirated in-cylinder direct injection gasoline engine, the influence of effective compression ratio and external EGR on engine fuel consumption was tested by adjusting the valve phase. The results show that the effective compression ratio has a significant impact on fuel consumption and its reduction can suppress knocking and improve fuel consumption. Within the tested working conditions, the low effective compression ratio can reduce fuel consumption by 2.7% and increase the thermal efficiency by 1%. However, too long intake duration leads to the release of more working substance after BDC, which affects the whole performance obviously. External EGR can improve the combustion process and advance the center of combustion. The fuel consumption rate reduces by about 6.8% when the EGR rate reaches 21%. However, the larger EGR rate will slow down the combustion process and significantly prolong the ignition delay and combustion duration. The too high temperature of EGR will also aggravate knocking and cause deterioration of fuel consumption.