Free fall gravity drainage is one of the most efficient mechanisms identified in the gas-invaded zone of naturally fractured reservoirs. It is believed that gravity drainage could result in very high displacement efficiency. In spite of this importunity, there is a lack of theoretical, experimental, and simulation works on investigation of this recovery process. In this study, a new approach is proposed for simulation of free fall gravity drainage called tank model approach. The commercial numerical simulator could be used as a platform to be able to perform this new approach properly. A simulator is selected as an appropriate environment since its fine grid simulation will lead to obtain the most proper results. The fine grid simulation as a numerical approach includes fewer simplifications comparing with available mathematical modeling and, consequently, the results are more accurate by considering numerical models. As a result, the tank model approach is properly performed for simulating the free fall gravity drainage process. Eventually, having the proper simulation of free fall gravity drainage could lead to obtaining a powerful tool for verifying the mathematical modeling introduced for description of this process. In addition, it could be used for statistical analysis in order to achieve better understanding of the block to block interaction, such as re-infiltration and capillary continuity phenomenon.