A symmetric-type UPS power system based on a nine-phase phase-shifting autotransformer, wherein comprising a three-phase AC power input terminal, a three-phase AC power output terminal, a nine-phase phase-shift autotransformer, a synchronized control device for controlling output of a three-phase inverter, a power-frequency isolation transformer and three circuits of output devices; wherein the nine-phase phase-shift autotransformer is a symmetric-type nine-phase phase-shift autotransformer, a three-phase AC input terminal of the nine-phase phase-shifting autotransformer is connected to the three-phase AC power input terminal; the nine-phase phase-shifting autotransformer is provided with three groups of three-phase AC output terminals, namely output terminals A1, B1 and C1 in an advance group, output terminals A0, B0 and C0 in an original group, and output terminals A2, B2 and C2 in a hysteresis group respectively; the power-frequency isolation transformer is provided with three groups of three-phase input terminals, namely input terminals U1, V1 and W1 in an advance group, input terminals U0, V0 and W0 in an original group, and input terminals U2, V2 and W2 in a hysteresis group respectively; the output terminals U, V and W of the power-frequency isolation transformer are connected to the three-phase AC power output terminal; the three circuits of output devices are an output device in an advance group, an output device in an original group and an output device in a hysteresis group; the output device in an advance group comprising a zero-sequence suppression commutating inductor in an advance group, a three-phase six-pulse rectifier in an advance group, a three-phase inverter in an advance group and a filter inductor in an advance group which are connected to each other in sequence; three-phase input terminals of the zero-sequence suppression commutating inductor in an advance group are connected to the output terminals A1, B1 and C1 in an advance group; three-phase AC output terminals of the filter inductor in an advance group are connected to the input terminals U1, V1 and W1 in an advance group; the output device in an original group comprising a zero-sequence suppression commutating inductor in an original group, a three-phase six-pulse rectifier in an original group, a three-phase inverter in an original group and a filter inductor in an original group which are connected to each other in sequence; three-phase input terminals of the zero-sequence suppression commutating inductor in an original group are connected to the output terminals A0, B0 and C0 in an original group; three-phase AC output terminals of the filter inductor in an original group are connected to the input terminals U0, V0 and W0 in an original group; the output device in a hysteresis group comprising a zero-sequence suppression commutating inductor in a hysteresis group, a three-phase six-pulse rectifier in a hysteresis group, a three-phase inverter in a hysteresis group and a filter inductor in a hysteresis group which are connected to each other in sequence; three-phase input terminals of the zero-sequence suppression commutating inductor in a hysteresis group are connected to the output terminals A2, B2 and C2 in a hysteresis group; three-phase AC output terminals of the filter inductor in a hysteresis group are connected to the input terminals U2, V2 and W2 in a hysteresis group; the synchronized control device is provided with four groups of sampling input terminals respectively connected to the three-phase AC power input terminal, the output terminal of the three-phase inverter in an advance group, the output terminal of the three-phase inverter in an original group and the output terminal of the three-phase inverter in a hysteresis group; the synchronized control device is provided with three groups of control output terminals respectively connected to the control terminal of the three-phase inverter in an advance group, the control terminal of the three-phase inverter in an original group and the control terminal of the three-phase inverter in a hysteresis group.