Abstract: Stability analysis is a crucial step in the design process for rotating machinery’s rotordynamics properties, which include static stability and dynamic stability. Static stability means that the rotor must be stable within the radius clearance formed with the stationary parts under normal operating conditions, and the system must be resistant to external disturbances. Besides, the rotor must smoothly pass multiple orders of critical speed while accelerating to the operating speed in order to achieve dynamic stability. In fact, dynamic parameters such as stiffness and damping coefficients are important indicators influencing the stability of high-speed rotating machinery, and the installation of an oil film damper assembly to the rotor has proven to be a reliable strategy for ensuring and optimizing system stability. In contrast to the motion form of a standard sliding bearing’s journal section, the damping mandrel of an oil film damper normally whirls around its pivot point in the form of a conical pendulum, i.e., the damping mandrel’s radial displacement and tangential velocity are linearly distributed along its axis, resulting in a wedge-shaped oil film clearance between the damping mandrel and the shell. As a result, oil film force and supporting parameters differ between the damper and the bearing. Therefore, when calculating and designing the supporting parameters of an oil film damper, the effect of wedge clearance on the damper’s supporting properties should be considered. This study firstly proposed a modification to the traditional Reynolds equation for characterizing the oil film pressure distribution when considering the wedge clearance, and the specific form of the equation was derived by adding items corresponding to the eccentricity and velocity distribution caused by this clearance. Next, the finite difference method based on successive over-relaxation was used to solve the modified problem iteratively. In order to verify the accuracy of the calculation results, the article contrasted them to ANSYS Fluent calculation results and previous experimental results. After comparison, it is discovered that the calculation results are in good agreement with the other two results, proving the dependability of this calculation method, which can make parameter setting more convenient and reduce calculation time. Finally, the oil film pressure distribution was computed under various parameter settings that characterize the wedge clearance. Using calculation tools of numerical integration and regression analysis, the function expressions for the relevant supporting property parameters and the corresponding linearized values were obtained. In summary, the calculation results demonstrate that while assessing the dynamic properties of oil film dampers, the effect of wedge clearance has to be taken into account. The calculation tool based on the modified Reynolds equation can improve computation efficiency and serve as a reference point for damper performance research and optimization.