Taking the lightweakening and antiglare design of an expressway tunnel portal in Gansu, China as an example, the authors make the comparative analysis on the operational performance of different kinds of lightweakening structures at tunnel portal. The analysis results show that lightweakening shed can not only solve the problem in the transition section of lightweakening, but also has antiglare effects. Then, the authors, by analyzing on two adverse working condition, put forward that  20°angle of incidence is the angle that induces the glare of drivers, and the points to which attention should be paid for lightweakening shed design, such as arch ribs interval, circumferential spacing of aluminium alloy pipes and luminance.