This paper proposes a switching scheme by controlling the inverter in the UPS to meet the demand of uninterrupted power supply for important load. It can make the load such as inductor motors get supplied by the stand-by power after power failure quickly and smoothly. The operational mechanism of the inductor motor is analyzed and the variation of the residual voltage and the influence factors of the impact current are explained. The inverter in the UPS is in Space Vector Modulation (SVPWM), which can immediately track the residual voltage to support the motor. It controls the phase of the output voltage of the inverter toward the stand-by power and makes the switching of the power supply smooth. This phase control scheme can make the power switch for the inductor motor succeed avoiding the impact of the surge current when the phase difference exists. The validity and the feasibility are convinced by the theoretical analysis and the simulation by Simulink as well as experiments in the laboratory.