Tunnel excavation construction method in flysch stratum

The invention relates to a tunnel excavation construction method in a flysch stratum. A tunnel is excavated in the flysch stratum by adopting a cantilever tunneling machine; a laser beam is adopted toshine on a tunnel face so as to identify the design excavation contour of the tunnel in real time; an initial hole is excavated first, and then fine excavation of the tunnel design contour line is conducted; and a protecting steel frame is erected on the inner side of a reserved reinforcement net of a previous supporting cycle. The tunnel excavation construction method has the beneficial effectsthat laser guiding is adopted to avoid back break caused by blind excavation; the excavated contour quality and excavation efficiency can be improved through the method and order of cutting rock by the cantilever tunneling machine, and collapse caused by oxidation of the flysch stratum can be effectively avoided; a protecting measure is adopted for the reserved reinforcement net of the previous cycle, and the construction