In this paper, a dimensionless parameter K = b/c, defined as the ratio of the yoke window height to the winding window width, is introduced to characterize the aspect ratio of the yoke in magnetic-shielded hollow current-limiting reactors. This parameter effectively reflects the combined influence of magnetic loading and structural stiffness on the vibration behavior of the yoke. A three-dimensional electromagnetic–structural coupled simulation model is established to investigate the effects of key geometric parameters on yoke deformation. The simulation results show that increasing the yoke window height reduces the magnetic flux density and thus decreases the maximum deformation, whereas increasing the winding window width weakens the structural stiffness and enlarges the deformation. When the aspect ratio K is kept constant, the maximum deformation remains within a stable and narrow range, indicating that K is a meaningful eigenvalue for describing vibration characteristics. This study provides practical guidance for selecting appropriate yoke dimensions and demonstrates that maintaining a reasonable aspect ratio K can help achieve balanced structural compactness and vibration control in magnetic-shielded hollow current-limiting reactors.