A single-phase online uninterruptible power supply topology comprising a main power circuit and an auxiliary power circuit, characterized in that: the main power circuit consists of an input stage, a power conversion stage, and an output stage connected successively; and the auxiliary power circuit consists of a charger, a battery and a DC/DC converter connected successively; wherein the input stage of the main power circuit includes a first capacitor and a first inductor; wherein the power conversion stage of the main power circuit includes first to fourth series branches connected in parallel between a positive bus (+BUS) and a negative bus (-BUS), the first series branch consists of a first diode and a second diode connected in series, the second series branch consists of a second capacitor and a third capacitor connected in series, a first switch is connected between an intermediate node of the first series branch and an intermediate node of the second series branch, the fourth series branch consists of a fifth switch and a sixth switch connected in series, the second switch is connected between the intermediate node of the second series branch and an intermediate node of the fourth series branch; wherein the output stage of the main power circuit includes a second inductor and a fourth capacitor; wherein an input of the charger of the auxiliary power circuit is connected to an AC input or positive and negative buses (+BUS, -BUS) of the uninterruptible power supply, characterized in that the third series branch consists of a third switch, a fifth capacitor, a sixth capacitor, and a fourth switch connected in series successively, and the intermediate node of the second series branch together with a node between the fifth capacitor and the sixth capacitor are grounded, and the third switch and the fourth switch respectively have a third diode and a fourth diode connected in parallel, and an output of the DC/DC converter of the auxiliary power circuit is connected to a node between the third switch and the fifth capacitor and a node between the sixth capacitor and the fourth switch, and the capacity of the second capacitor and the third capacitor is substantively less than capacity of the fifth capacitor and the sixth capacitor. the main power circuit consists of an input stage, a power conversion stage, and an output stage connected successively; and the auxiliary power circuit consists of a charger, a battery and a DC/DC converter connected successively; wherein the input stage of the main power circuit includes a first capacitor and a first inductor; wherein the power conversion stage of the main power circuit includes first to fourth series branches connected in parallel between a positive bus (+BUS) and a negative bus (-BUS), the first series branch consists of a first diode and a second diode connected in series, the second series branch consists of a second capacitor and a third capacitor connected in series, a first switch is connected between an intermediate node of the first series branch and an intermediate node of the second series branch, the fourth series branch consists of a fifth switch and a sixth switch connected in series, the second switch is connected between the intermediate node of the second series branch and an intermediate node of the fourth series branch; wherein the output stage of the main power circuit includes a second inductor and a fourth capacitor; wherein an input of the charger of the auxiliary power circuit is connected to an AC input or positive and negative buses (+BUS, -BUS) of the uninterruptible power supply, characterized in that the third series branch consists of a third switch, a fifth capacitor, a sixth capacitor, and a fourth switch connected in series successively, and the intermediate node of the second series branch together with a node between the fifth capacitor and the sixth capacitor are grounded, and the third switch and the fourth switch respectively have a third diode and a fourth diode connected in parallel, and an output of the DC/DC converter of the auxiliary power circuit is connected to a node between the third switch and the fifth capacitor and a node between the sixth capacitor and the fourth switch, and the capacity of the second capacitor and the third capacitor is substantively less than capacity of the fifth capacitor and the sixth capacitor.