Research conclusions: The sloughing of the tunnel portal is not only related to the geological reason, but also to the unfaithful reconnaissance and unchanging the design scheme timely. Nowadays the main causes for the sloughing of tunnel portal are that the construction is not conducted according to the design, the construction scheme is not changed timely, the construction method is not suitable and the monitoring is not done on time. For the sloughing of tunnel portal, the following measures should be taken; the anchor bolt and steel gridding and spurt concrete are used if the thickness of the soft rock is less than and equal to Sm, the steel-pipe pile and grouting are adopted if the thickness of the soft rock is 5-10m, and the anti-slide pile should be adopted if the thickness of the soft rock is greater than 10m. At the same time, it is necessary to lay the secondary lining to the tunnel outside and tunnel portal.