Abstract: In order to eliminate reactive current and　improve power factor, Active Power Factor Correction(APFC) circuit is used in Uninterrupted Dynamic Voltage Restorer(UDVR). By controlling the switcher of the APFC circuit, the harmonic caused by rectifier can be eliminated, and the power factor can be improved to 1.A double close\|loop control strategy with inner current loop and outer voltage loop is used in single\|phase APFC circuit and its control circuit is simple and inexpensive.The open\|loop control strategy is used in inverter, and the same phase compensation is adopted to compensate voltage sag.MATLAB　simulation results show that the APFC Based UDVR can provide the loads with a pure and standard sine voltage wave and can also compensate voltage sag continuously.