In　recent　years,　with　the　wide　application　of　modern　power　electronic　equipments,　harmonic　pollution　in　electrical　power　system　becomes　more　and　more　serious.　As　the　primary　means　of　harmonic　suppression,　active　power　filter(APF)　has　been　drawing　more　and　more　attention.　The　working　principle　of　APF　is　described　in　detail　in　this　paper.　And　then　a　new　control　strategy　is　proposed　to　detect　the　harmonic　current　accurately　and　obtain　good　performance　of　current　tracking,　In　this　strategy,　the　fast　fourier　transform　algorithm(FFT)　method　is　used　to　detected　the　harmonic　current,　and　the　space　vector　pulse　width　modulation(SVPWM)　current　control　method　based　on　indeterminate　frequency　hysteresis　is　used　to　track　the　compensating　current.　The　results　of　simulation　and　experiment　have　shown　that　it　can　greatly　reduce　the　distortion　rate　of　the　grid　current　and　restrain　harmonic　pollution　of　the　grid.