Light transmission efficiency (LTE) is the most important parameter to evaluate the daylighting performance of light pipes. In the calculations of LTEs of light pipes, the cumulative effect of light polarization caused by several specular reflections in pipes is often neglected. Therefore, in order to make clear the cumulative effect of light polarization generated by continuous specular reflection, through optical theoretical analysis and formula derivations, after determining the influence of light polarization on the reflectivity of specular reflection materials, this article for the first time clarified the change rule of the reflectivity of interior surface of a light pipe with the number of reflections and the influence of the variation of reflectivity on the LTE of the light pipes. The results indicated that each time a light beam projects on the pipes inner surface, there will be a light polarization that produces different reflectivity on the two orthogonal components, i.e ρ⊥ and ρ‖ and ρ⊥≥ρ‖; In every reflection, the values of ρ⊥ and ρ‖ remains fixed, but the overall reflectivity will gradually rise with the increase of reflection times, so the light loss rate will continue to slow down. Finally, the LTE expression of a single beam in a light pipe is derived, which lays a theoretical foundation for the establishment of the LTE mathematical calculation models under complex light sources.