Abstract: In order to improve reliability of underground UPS power supply system, a dead-beat circulating current suppression method of underground UPS paralleling power supply system was put forward. Firstly, an equivalent discrete mathematical model of UPS paralleling power supply system topology was established, and zero sequence circulating current in paralleling power supply system was emphatically analyzed. Then, nonlinear dead-beat controller was introduced to control and process zero sequence current. Finally, verification and analysis of the method were done by prototype of 2×35 kW UPS paralleling power supply system. The experimental results show that the method can effectively inhibit zero sequence current of underground UPS paralleling power supply system，and realize redundancy restoration of UPS paralleling power system in 2-5 ms.