A new topology of on-line UPS based on Z-source inverter was proposed. The new topology could not only output a perfect sine wave under no industrial transformer, which decreased the volumetric size and cost of the UPS system, but could act on inductive loads besides capacitive ones. And a charging and discharging circuit based on Buck/Boost topology was added, where the battery's rated voltage could be smaller, which could reduce the power supply's volume and lessen the voltage stress of switch components. Moreover, an active power factor correction circuit based boost topology was provided in the topology' input, which could improve input power factor and reduce harmonic pollution. Simulation and experiment results were provided to verify the correctness and effectiveness of the new UPS.