Abstract: The unique secondary expansion stroke of a five-stroke engine improves thermal efficiency, and its unique performance characteristics make it suitable for range extenders.In order to explore the influence of timing and ignition time of a high/low pressure cylinder valve on the performance of a five-stroke engine, this paper establishes a one-dimensional model of a five-stroke engine based on GT-power, and uses the DOE tool to carry out a multi-objective optimization with the target of maximum power, minimum BSFC and minimum NOxemissions under limited torque conditions.The result indicates that properly increasing the valve overlap angle of the low pressure cylinder can reduce the exhaust flow loss and improve the efficiency of exhaust work.At last, each target value is optimized by 3.26%, 2.5% and 0.14% respectively.The application of multi-objective optimization to the parameter optimization of five-stroke engines ensures the variables in a feasible range realizes the improvement of multiple objectives.