The Imbert-Fedorov (IF) transverse shift originates from the spin Hall effect of light, which corresponds to the interaction between the orbital angular momentum and spin/polarization state of the photon. In this work we systematically investigate the IF transverse shift in a topological insulator slab structure with finite surface energy gap. We report on a systematic investigation of how surface magnetization orientation, topological magnetoelectric polarizability, and slab thickness influence the IF shift in a topological insulator slab for different surface energy gaps and incident polarization states. The IF shift is found to exhibit a non-monotonic dependence on the surface energy gap, identifying this gap as a key parameter for achieving significant enhancement. Furthermore, the specific gap value at which this peak enhancement occurs is found to shift slightly with variations in the slab thickness. Under the parallel magnetization on topological insulator surfaces, the IF shifts are much more significantly enhanced by increasing topological magnetoelectric polarizability, and the surface energy gap corresponding to the peak value of the IF shift moves toward narrower gap as the topological magnetoelectric polarizability increases. The magnitude of the IF shift under TM-polarized incidence is generally larger than that under TE- and elliptically polarized states. Examination of the combined effects of incident polarization and layer thickness reveals that, for specific surface energy gaps the peak positions of its thickness-dependent oscillations may drift as the polarization angle varies, and the direction of this drift is opposite under two distinct surface magnetization configurations. This indicates that the IF shift can be enhanced and effectively controlled through judicious optimization of the topological insulator surface energy gap, magnetization direction, and thickness. This work offers practical significance for designing high-performance optical devices and highly sensitive measurement systems based on the transverse shifts in topological materials.