Carbonate reservoirs are one important type of reservoirs in the Middle East, mainly composed of marine porous deposit. Rich gas flooding can further improve the injectivity and the recovery factor in carbonate reservoirs. Therefore, a numerical simulation model considering fluid distribution characteristics is established to clarify the reservoir fluid distribution characteristic after rich gas injection. Then the gas component at different production times and different areas are analyzed. The tracer method is used to mark the various components of injected gas, accurately reflecting the distribution characteristics of injected gas in the reservoir. Based on the coupling effect of reservoir fluid components and injected gas components, the Minimum mixing pressure (MMP) during rich gas flooding process is characterized. The simulation results show that the distribution characteristics of injected hydrocarbon gas in the reservoir are related to the proportion of components in the injected gas. A large number of injected rich gas mainly gather at the root of the horizontal injectors. This can increase the recovery factor of surrounding area and also bring high earlier gas breakthrough risk. After rich gas flooding, the overall composition of the reservoir liquid phase shows a trend of increasing intermediate hydrocarbon components. The reservoir fluid is enriched, and the change degree gradually decreases along the direction from injection wells to production wells. Due to the high output of light hydrocarbon components after rich gas injection, the proportion of heavy hydrocarbon components will increased also. The line analytical method results show the mixed fluid during rich gas flooding is mainly caused by vaporizing gas multiple-contact miscible process. The MMP pressure rises and exceeds the reservoir pressure, which cannot meet the miscibility requirements and presents a non miscibility state.