Abstract: The Gaoligong Mountains, part of the Hengduan Mountain Range, present highly complex engineering geological conditions. Deep-buried tunnels traversing the Gaoligong Mountains are likely to encounter a range of adverse geological issues, including high geothermal gradients, elevated ground stress, active fault zones, rock bursts, large-scale deformations, and water or mud inflow. Based on geological mapping and engineering survey data from the ongoing ultra-long, deep-buried highway tunnel in the Gaoligong Mountains, a detailed analysis of the geological environment, engineering geological characteristics, and the primary adverse geological issues has been conducted. The study reveals that the main fault zones within the tunnel construction area control the distribution of rock masses, hydrothermal activity zones, and groundwater circulation patterns. These faults may result in hazards such as fault-induced water inrush and high-temperature thermal damage when the deep-buried tunnel intersects them. A comprehensive analysis indicates that high-temperature thermal hazards are the most critical factor constraining tunnel construction. The primary causes of elevated geothermal conditions are hydrothermal activity and active faulting, with the most vulnerable areas being fault-related water-conducting zones and lithological contact zones. Additionally, high ground stress presents a significant challenge to the stability of the surrounding rock mass, particularly in sections of the tunnel with burial depths exceeding 620 m, where there is a moderate risk of rock bursts and localized high-risk areas. The findings of this study provide valuable insights for understanding adverse geological conditions in deep-buried tunnels under similar engineering geological environments.