Abstract: To solve the problem of voltage sag, Dynamic Voltage Restorer (DVR) is used to compensate load voltage instantly based on active hybrid energy storage system, and its equivalent circuit is presented.Both the mathematical model and the control system of the ultracapacitor/battery hybrid system are set up, which improves whole working characteristic and economy of DVR.Simulation and analysis on DVR with active hybrid energy storage system are carried out, and the results show that this active hybrid energy storage system can effectively maintain the voltage level of sensitive load as to long\|duration power interrupts and frequent voltage sag.