The active power filter(APF) is a novel method of dynamic harmonic suppression.The compensation performance of APF is determined by the link of detection and control.At the same time,the voltage balance control is the prerequisite for APF to work normally.The detection method of harmonic current based on sliding-window iterative algorithm of DFT is described.And a DC side capacitor voltage control strategy is proposed based on each phase split current.The design method of PI parameter for voltage loop from the perspective of power balance.The correctness of sliding-window iterative algorithm of DFT and proposed DC voltage control strategy is verified by simulation and experiment.