The present invention provides an active compensation device that is connected between a power system and a non-linear load in parallel for providing an instantaneous compensation current for the non-linear load. The active compensation device comprises an electricity-storing unit, a bridge switching unit, and a controlling unit. The bridge switching unit is connected electrically with the electricity-storing unit for charging or discharging the electricity-storing unit; the controlling unit is used to produce control signals to switch the bridge switching unit. The electricity-storing performs a dual-direction current operation by means of switching the bridge switching unit to compensate the power system so as to increase instantaneously the current capacity.