The models of polyethylene terephthalate (PET) non-circular cross-section (NCCS) fibers were established, and the characteristic parameters of non-circular cross-section fiber used in this numerical simulation were extracted. Furthermore, the differences of refracted light intensity ratio Irz and the direction of refracted light βt among circular, trilobal and quadri-lobal cross-section fibers were analyzed theoretically. The results show that the refracted light intensity ratios Irz of these fibers were in the range of 0.94~0.95. Both the trilobal and quadri-lobal cross-section fibers' βt, which was the angle of refracted light to Y-axis, changed non-monotonically and much more intricately than that of circular cross-section ones. Moreover, according to the theory of geometrical optics, the effects of trilobal and quadri-lobal cross-section shapes on the changes of internal refracted light and transmitted light in fibers were also conducted. The results suggested that the refracted and transmitted light were changed more effectively in the quadri-lobal cross-section fiber. The results of the experiment show that the shielding properties of quadri-lobal cross-section filament fabrics were better than that of the counterparts with circular fibers, but the difference was limited or insignificant.