The invention relates to the technical field of uninterruptible power supplies, specifically to a high-frequency dual-conversion uninterruptible power supply system using flywheel energy storage and acontrol method thereof. The uninterruptible power supply system comprises a dual-conversion UPS high-frequency device arranged between an AC input terminal and an AC output terminal, and a flywheel energy storage device connected with the dual-conversion UPS high-frequency device. The invention discloses a high-frequency double-conversion type uninterruptible power supply system using flywheel energy storage. The flywheel energy storage device comprises a DC-AC bi-directional converter and a flywheel energy storage unit , a DC-DC converter does not need to be arranged in the dual-conversion UPS high frequency device, the efficiency of the double conversion type UPS high frequency device is increased, At that same time, the cost of the double-conversion type UPS high-frequency device is reduced, the volume of the double-conversion type UPS high-frequency device is reduced, there is no communication connection between the double-conversion type UPS high-frequency device and the flywheelenergy storage device, the system wiring is simplify, the dependency between the devices is reduced, and the compatibility of the system is enhanced.