According to conditions of landform in mountain area and features of mountainous road network, a concept of mountainous characteristic I Shaped road network was presented. By adopting time cost analysis method, finite impact ranges of key pathway and its adjoining pathway surrounding road networks were defined. Using graph theory and fluid network theory, the analysis of pathways to mountainous characteristic I Shaped road network was carried out. With the ways of virtual node and virtual branch, pathway algorithm of mountainous characteristic I Shaped road network was provided. The calculated process of the analysis of pathways to mountainous characteristic I Shaped road network was illustrated through numerical example, which shows that it provides guidance for determining an optimal route to evacuation and evacuation management in the calamity events.