Cyclic gas injection is considered as an effective and quick responding recovery process that has been widely used in the worldwide. Studies showed that cyclic gas injection combined with modem technologies such as horizontal well drilling and hydraulic fracturing has achieved promising results in low permeability formation. Cyclic gas injection technique was introduced in our earlier publication for improving oil recovery in stimulated fractured shale oil reservoirs. In this paper,we focus on the effect of injected gas composition and fracture properties on oil recovery. Different injection gas scenarios such as lean gas,rich gas and CO2 were included in the simulation in order to analyze the EOR mechanisms of vaporizing,condensing or a combined condensing/vaporizing process. Our simulation results indicate that the stimulated natural fractures are critical to enhancing oil recovery and well productivity performance in shale oil reservoirs. Since the interaction of the induced hydraulic fractures with pre-existing natural fractures and fissures makes the hydraulically fractured reservoir modeling very challenging in shale oil/gas reservoirs,we can use a dual-continuum model by making changes to the fracture permeability and intensity to attain a better characterization of the natural fractures. We conclude that cyclic gas injection in shale oil reservoirs employing hydraulically stimulated fractures is feasible to improve substantial amounts of oil production than primary production.