Abstract: To accurately invert the physical properties of reservoirs after acid injection, this paper establishes a well test interpretation model based on oil-water two-phase flow theory, which comprehensively considers the distribution characteristics of oil and acid during the acidizing process. The oil-water transition zone is characterized by multiple radial zones with different properties. The saturation in the transition zone is calculated using the Buckley-Leverett equation, while the relative permeability, viscosity, and total compressibility are derived based on this saturation. The model is first dimensionlessized. The flow equations are then transformed into Laplace space using the Laplace transform, where a solution matrix is constructed to obtain the solution. The Stehfest numerical inversion algorithm is subsequently used to convert the Laplace-space solution back to real space. To further explore the model's practicality, the pressure response characteristics under various injection and formation conditions are investigated. The study shows that using multiple zones to represent the oil-water transition zone is feasible. Influenced by the fluid properties, the aquifer, oil-water transition zone, and oil zone exhibit distinct pressure response features, enabling the inversion of reservoir parameters. The model was applied to fit actual pressure data from an acid injection well test in an oilfield, and the results align with the field understanding of the well. The established well test interpretation model holds significant importance for understanding reservoir characteristics in the early life of a well.