Abstract: The invention relates to a two-input uninterruptible voltage converting device and a method thereof. The device comprises a first conversion circuit, a second conversion circuit, an energy storage unit, a fly-wheel switch tube and a control unit. The method comprises the following steps of: converting a PWM signal outputted by a pulse width modulator into first, second, third and fourth PWM signals in phase via a pulse transformer; driving the first conversion circuit and the second conversion circuit respectively to operate synchronously; converting a high voltage DC (Direct Current) and a low voltage DC into two pulse voltages in phase to adaptively perform mutual energy compensation via an intersection; and supplying a load with an uninterruptible stable voltage via the back-end energy storage unit and free-wheel circuit. The two-input uninterruptible voltage converting device has the advantages of high circuit conversion efficiency, high reliability and low power consumption.