In this paper, the typical diseases of 17 tunnels in the Zhubalong to Dongjiu section of the Sichuan-Xizang Highway on the National Highway 318 were systematically investigated and analyzed in depth. The investigation results show that the tunnel diseases mainly include the hollowing out of the foundation of the riverside side of the open-cut tunnel, the leakage of the lining (point, line, surface, and construction joint seepage), the lining cracks, the pavement cracks and seepage, and the blockage of the drainage system. Based on the causes of the disease, this paper proposes a multi-dimensional treatment design scheme covering the hole, lining, pavement, and drainage system. It is verified by field implementation that the proposed treatment measures effectively control the development of the disease, significantly improve the operation status of the tunnel, and achieve good engineering results. This study provides valuable engineering practice experience and reference for the accurate diagnosis and efficient treatment of tunnel diseases under similar complex geological conditions of the Sichuan-Xizang Highway.