The invention relates to an uninterrupted power system, comprising an accumulator, and also comprising a monitoring circuit, a controllable switch and a current transformer, wherein the monitoring circuit is used for monitoring whether electric supply is normal, outputting a first monitoring signal when the electric supply is normal and outputting a second monitoring signal when the electric supply is abnormal; the input end of the controllable switch is connected with the electric supply, and the output end of the controllable switch is connected with a load through a common connection point; the control end of the controllable switch is connected with the monitoring circuit; the controllable switch is switched on under the control of the first monitoring signal, and switched off under the control of the second monitoring signal; the current transformer performs reactive and harmonic compensation under the control of the first monitoring signal; and the current transformer outputs current under the control of the second monitoring signal to power the load for normal operation. The uninterrupted power system is high in energy efficiency index and can meet the power supply requirement of the load in continuous operation. The invention also relates to a control method of the uninterrupted power system.