According to the present invention, provided is a watchdog system for Uninterruptible Power Supply (UPS), and auto recovery method using the same. In case the power supply path of UPS is switched from the normal power line to the bypass line, the UPS watchdog system of the present invention is firstly compulsively recovers again the power supply path to the normal power line for given times and, nevertheless, in case it is not recovered, the power is supplied through the bypass line. Accordingly, in case the power supply path is switched to the bypass line due to the temporary disorder of UPS, it can be rapidly recovered to the normal power path, so that the power supply by the UPS apparatus can be more stably performed.