Abstract: The effects of compression, cut-off and pressure ratios on the performance of a dual cycle during the finite-time thermodynamic are investigated. In the model, the linear relation between the specific heat ratio of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston and the heat transfer loss are considered. The relations between thermal efficiency and compression ratio and between an Ecological Coefficient of Performance (ECOP) and compression ratio are derived. Moreover, the effects of cut-off and pressure ratios on the cycle performance are analyzed. The results show that the cut-off and pressure ratios are more effective on performance of a dual engine. Also, the points of maximum ECOP and thermal efficiency of dual cycle will decreases with an increase of cut-off and pressure ratios. The results are of importance to provide good guidance for the performance evaluation, improvement and design of practical dual engines.