In order to develop a special extended-range engine, the performance simulation model of a 2.0 L gasoline engine was established by using GT-power software. Through thermodynamic simulation calculation and analysis, the valve lift curve and valve timing are optimized to realize Atkinson cycle. The performance indexes such as engine power, torque and fuel consumption are predicted, and the recommended scheme of engine valve timing is put forward. The results show that the model can provide technical support for engine forward development and performance simulation analysis.