The invention discloses a tunnel digging-out supporting structure and a construction method thereof. The supporting structure includes upper steps and lower steps. The upper steps and the lower stepsare arranged on the entrance of a tunnel, a connecting slope is connected between the upper steps and the lower steps, small
pilot tunnels are formed in the upper steps, the supporting structure further includes a temporary support, an advanced support, a
system anchor rod, a foot-locking anchor rod and a preliminary support, the temporary support is arranged around the small
pilot tunnels, the advanced support, the
system anchor rod, the foot-locking anchor rod and the preliminary support are used for reinforcing surrounding rock around the tunnel, the supporting structure and also includes alarge
pipe shed guiding wall and a large
pipe shed, and after the small
pilot tunnels are dug out, the small pilot tunnels are out, the large
pipe shed guiding wall and the large pipe shed are constructed from outside to inside in the entrance of the tunnel; according to the construction method, benching stepping method is adopted to construct adjacent entrance sections; the advanced small pilottunnels are excavated on one side of the upper steps, the advanced support, the
system anchor rod, the foot-locking anchor rod, the preliminary support and the temporary support are constructed, and the small pilot tunnels pass through to the entrance of the tunnel; the large pipe shed wall is constructed, holes are drilled in the large pipe shed wall, and the large pipe shed advanced support is provided; and the small pilot tunnels on the other side of the upper steps of the support are excavated from the holes to the entrance, the temporary support of the small pilot tunnels is dismantled, the lower steps of the support are excavated to the entrance.