Landing gear for small aircraft require a wide range of damping forces, depending on the speed of fall and road conditions. Conventional passive landing gears are difficult to satisfy in various situations. A semi-active MR damper was applied to the aircraft. In order to obtain high damping force, the magnetic field strength at the stimulus generated when the current is applied must be strong. In this study, the MR damper was mathematically modeled based on Baron 55 model, which is a passive landing gear, considering the damping force and geometrical constraints required for small aircraft, and Gauss’ magnetic law. Magnetic field analysis was performed by finite element method using Ansys Maxwell software. The damping force region of the controllable MR damper was identified by using the magnetic field strength obtained through the analysis.