The terrain of mountainous areas is high and undulating. This leads to high filling and deep excavation in the construction of mountain roads. The quality and safety risk of high fill and deep excavation construction is greater. If the construction treatment or subsequent treatment is improper, it is very easy to cause engineering diseases. Based on this, this paper takes the characteristics of high fill and deep excavation special subgrade projects in mountainous areas as the breakthrough point to explore the particularity of the project. Then, from the perspective of the disease mechanism of high fill and deep excavation subgrade, this paper analyzes the internal logic of common diseases such as subgrade settlement deformation, slope instability, damage, and destruction. Finally, the paper summarizes the key technologies for the treatment of high fill and deep excavation special subgrade in mountainous areas, and the disease problems and mechanism of anchored high fill and deep excavation subgrade. And it explores the effective disease treatment technology to ensure the high-quality development of Highway Engineering in mountainous areas.