In order to solve the problems of multiple influencing factors, different focuses of participating parties, and inability to quantitatively describe the comparison and selection schemes in the current process of selecting routes for mountainous expressways, based on thorough research on the influencing factors of expressway and railway route selection at home and abroad, the influencing factors of expressway route selection in mountainous areas of China were systematically analyzed and summarized, and four aspects: economy, technology, safety and environment were summarized, totaling 16 specific influencing factors. Based on the Xihe to Tanchang Expressway project, a group of 164 experts from the local government, industry regulatory departments, owners, design, construction, supervision, third-party testing units, and research institutes in the project area were organized to form an expert group. The analytic hierarchy process (AHP) was used to evaluate the importance of 16 route selection influencing factors. The results show that the comprehensive weight average score of the three influencing factors in the environmental indicators is high, reflecting the further strengthening of environmental awareness in the field of engineering construction. To further establish a optimization model for scheme comparison, taking the scheme comparison of the route from the project Dengta Village to Haolin Village as an example, the technique for order preference by similarity to idea solution (TOPSIS) method based on the AHP was used to compare and select schemes. The superiority of the four comparison schemes is 2.84, 0.56, 0.72, and 2.15, respectively, indicating that scheme 1 is optimal. Based on a comprehensive analysis of the factors affecting the selection of mountainous expressway routes, the research results adopt the AHP-TOPSIS comprehensive evaluation index system model. While fully utilizing expert experience, it can objectively and scientifically compare the selection schemes for optimal solution ranking, effectively solving the problem of mountainous expressway route selection and providing reference for the selection of similar linear engineering schemes.