[Objective] Mobile energy storage systems （MESS） offer both energy supply and spatial dispatch flexibility. This paper proposes a pre-allocation and optimal scheduling framework for MESS that explicitly considers power-transportation coupling， aiming to safeguard critical loads and optimize system operation under multi scenarios. [Methods] The power and transportation network are modeled as weighted undirected graphs coupled through charging/discharging facility nodes. A comprehensive modularity index is introduced for regional partitioning， ensuring strong electrical connectivity and high traffic accessibility within each partition. A bi-level optimization model is constructed to determine warehouse pre-allocation of MESS and optimize multi-scenario routing and charging/discharging scheduling strategies. The shortest-path preprocessing method is employed to accelerate solution performance. [Results] Case studies on a modified IEEE 33-bus distribution system and the Sioux Falls 24-node transportation network verify the proposed method. The results show that the proposed framework achieves reasonable spatial allocation and flexible dispatch of MESS. Compared with partitions based on single electrical or traffic indicators， the comprehensive modularity-based partitioning better reflects power-transportation coupling characteristics. The bi-level optimization model significantly improves MESS scheduling efficiency and enhances the supply capability of critical loads under multi-disaster conditions. [Conclusions] The proposed method provides theoretical support for the planning and operation of MESS by leveraging both spatial flexibility and cross-domain coordination.