Due to the low permeability and strong heterogeneity, water flooding cannot effectively maintain a stable oil production and achieve a good recovery performance in a tight conglomerate reservoir of M oilfield. As an efficient tertiary oil recovery technique, CO2 injection is considered as an important potential method to improve the production performance for such tight conglomerate reservoir in this area. In this work, a systematic research pertaining to different CO2 recovery method is experimentally conducted aiming to examine the feasibility of CO2 EOR method in the tight conglomerate reservoir of M oilfield. To be specific, effects of miscibility and CO2 injection processes (CO2 flooding or huff-n-puff) on oil recovery performance are quantitatively analyzed and assessed. The results show that a maximum displacement efficiency of 81% can be reached under a 33 MPa CO2 injection pressure, above the minimum miscible pressure (26 MPa), in M oilfield. Noted that the displacement efficiency is positively correlated with injection pressure, which apparently affects the degree of miscibility. Under immiscible condition, the oil displacement efficiency can reach around 50% with an injection pressure of 77% MMP, a 38% decrease from maximum miscible flooding displacement efficiency. Similarly, the higher the injection pressure, the higher the recovery efficiency. Under condition of 30 MPa injection pressure, the recovery factor CO2 huff-n-puff is about 52%, which is slightly higher than immiscible CO2 flooding, but much lower than miscible CO2 flooding. The research results provide an important reference for the optimization of CO2 injection development mode in the tight conglomerate reservoir.