The invention relates to a mobile energy storage power supply system access quit control method under uninterruptible power supply. A mobile energy storage power supply system topology structure is provided. If the mobile energy storage power supply system topology structure is a two-level topology structure, an alternating current-direct current conversion part is composed of two sets of PCS. The battery side PCS alternating current side is connected with a power grid. The direct current side is connected with an energy storage system. The load side PCS alternating current side is connected with a load. The direct current side is connected with the energy storage system. The energy storage system is connected with the direct current side of the alternating current-direct current conversion part. A mobile energy storage power supply system and a power grid fast interface are divided into a series interface cabinet and a parallel interface cabinet. Different control methods are used to realize fast access and quit of the mobile energy storage system. According to the invention, the provided interface technology can realize fast access of the mobile energy storage system under the condition of uninterruptible power; fast quit of the system is realized after the power supply work is completed; the workload of operation and maintenance personnel is reduced; the work efficiency is improved; and uninterrupted power supply to the load is ensured.