Abstract: The high-voltage transformer-less battery energy storage system (BESS) adopts the concept of cascading H-bridge circuits to connect the high-voltage power grid. A large number of battery cells are separated equally into numerous clusters at the DC side of H-bridge submodules, and a high degree of modularity features the BESS. Compared with the low-voltage solution, it has obvious advantages, such as a larger capacity for a single machine, higher efficiency, and faster response speed. As a high energy density energy storage medium, the safe and stable operation of lithium battery highly depends on the reliability of battery core. In the traditional fault-tolerant control of battery cluster, the whole submodule is removed by setting AC bypass switch directly. This strategy requires additional redundant modules, which increases the energy storage cost. Due to the limitation of modulation ratio, the number of modules exiting the battery cluster fault is limited, and the capacity utilization rate of the system is not high. In this paper, the fault-tolerant strategy of battery cluster is proposed to remove the faulty battery cluster by DC circuit breaker, and switch the faulty module from the active charge-discharge mode to the reactive fault-tolerant mode, so as to give full play to the power grid voltage support capability of the faulty module. The proposed control strategy can realize the withdrawal of any number of modules, and other sub-modules can continue to store or release energy, which is of great significance to improve the utilization rate of system capacity at the end of charge and discharge.