The invention discloses a supporting method for supporting a tunnel. The supporting method for supporting the tunnel comprises the following steps that S001, a thin bedrock region is determined through a geophysical exploring method, and geological outline of the thin bedrock region is analyzed; S002, parameters of anchor rods used for supporting top plates of the tunnel in the thin bedrock region are determined according to the analyzed result of S001, and the anchoring rods are hit into the top plates of the tunnel in the thin bedrock region; S003, parameters of anchor ropes used for supporting the top plates of the tunnel in the thin bedrock region are determined according to the analyzed result of S001, and the anchoring ropes are hit into the top plates of the tunnel in the thin bedrock region; S004, steel strips and metal nets are arranged on the tunnel walls of the two sides of the tunnel in the thin bedrock region; and S005, real-time monitoring for condition of the tunnel is kept. According to the supporting method for supporting the tunnel, by utilizing an optimum composite beam theory, the lengths of the anchor rods and the anchor ropes as well as installing stress of an anchor rod system are designed, and the anchor rod system with the optimum composite beam is achieved.