The GT-power simulation model was established thereby using a 3-cylinder direct-injection gasoline engine as the research object and the simulation model was further calibrated according to the bench test data. Based on the fuel economy, the evaluating and research for the engine key technologies were conducted under the high efficiency conditions of 1.4MPa and 3000r/min by using the simulation model. The results showed that different key parameters had different sensitivities to brake specific fuel consumption, among which the sensitivity of compression ratio was the largest and the sensitivity of Miller degree was the smallest. The weight of key technology on fuel economy was obtained, in which the high compression ratio technology took 70%, VVT technology took 20%, Miller cycle technology took 7% and EGR technology took 3%. The interaction between key technologies and the specific performance were clarified.