Abstract: Under complex geological and geostress conditions, the design of mountain-adjacent tunnels in hard rock areas faces numerous challenges, particularly in determining the tunnel's buried depth. This study proposed a method for determining the buried depth of mountain-adjacent tunnels, comprehensively integrating high-level tectonic stress, the superimposed effects of valley stress fields, and the potential for rockbursts triggered by depth. The specific methods include: (1) Determining the influence range of the superimposed tectonic stress field and valley stress field. This involves initially estimating the influence depths of the tectonic stress and valley stress fields based on measured geostress data from boreholes in the slope zones of canyon areas, and then uses numerical simulation technology to optimize the preliminary estimation results to ensure the accuracy and reliability of the initial obtained range. (2) Determining the limit of severe rockbursts caused by burial depth. Firstly, it calculates the statistical mean value of saturated uniaxial compressive strength (R_c) by rock physical and mechanical tests in the tunnel site area, and then selects the typical geological section of the tunnel site to simulate the stress field. It uses the strength stress ratio method, introducing the σ_max=R_c/2 as the basis to judge whether the buried depth may cause severe rockbursts. (3) It should be emphasized that on the basis of the above two steps, the relatively safe buried depth range of the tunnel is determined, while the deep buried depth section (≥1200 m) should be minimized as far as possible in the design process to achieve the final optimization of the tunnel buried depth. This study provides a scientific basis and practical method for the buried depth design of hard rock mountain-adjacent tunnels, and has a wide application prospect and popularization value in the future design of mountain-adjacent tunnels.