Abstract: The energy consumption density of long- and large-scale tunnels is much higher than other transportation infrastructure. The high energy consumption characteristic causes high pollution and high carbon emission problems. Considering the regulation characteristics of energy storage and the underground space development foundation of tunnel projects, this paper designs a framework of tunnel intelligent power system and proposes an optimal planning method of energy storage capacity for low-carbon transition of tunnel power systems. First, the tunnel intelligent power system framework is designed based on multiple power complementation, active load coordination and two-way interaction between supply and demand. And by comparing the advantages and disadvantages of ground and underground energy storage schedules in intensive utilization of land resources, coping with environmental constraints and weakening the harm of energy storage failure, the construction scheme of underground energy storage is clarified. Then, a bi-level optimal planning method of energy storage capacity is proposed by analyzing the coupling effect of energy storage capacity planning and tunnel intelligent power system dispatching strategy. Finally, the examples are adopted to analyze the effectiveness of proposed tunnel intelligent power system framework and optimal planning method of energy storage capacity, and the notable advantages of underground energy storage scheme in terms of economy, low carbon and social benefits are compared and verified.