The on-load tap changer is the core component of the transformer. During the operation of the on-load tap changer, the moving and fixed contact system of the switching mechanism collides and closes quickly after the release of the energy storage of the fast mechanism. This violent collision inevitably produces the scattering of metal particle defects. In order to study the influence of metal particles on insulation, it is necessary to carry out the simulation experiment of metal particle defect motion in the oil chamber of on-load tap changer. In order to carry out the experiment effectively, this paper proposes a method to estimate the motion state and rising height of the simulated motion of metal particle defect with the increase of oil flow. The size of metal particle defect and the velocity of oil flow can be used to estimate the rising motion state and maximum height, and reduce the experimental difficulty of the study of metal particle defect motion induced discharge in the oil tank of on-load tap changer.