In　dealing　with　the　problem　of　the　SAPF＇s　nonlinear　and　strong　coupling　model,　the　internal　model　control　of　three-phase　four-leg　active　power　filter　based　on　online　ANN　method　is　studied　in　this　paper.　With　the　ANN＇s　nonlinear　mapping　ability　of　self-learning　and　self-organizing　modeling,　the　inverse　system　can　be　approximated　by　online　LS-SVM.　In　order　to　have　a　good　linearization　control　effect,　the　internal　model　control　based　on　ANN　is　proposed　for　the　combined　pseudo-linear　system.　This　method　can　be　used　to　design　effective　controllers　for　nonlinear　system　with　unknown　mathematical　models.　At　last,　the　simulation　results　show　that　a　good　steady-state　performance　can　be　obtained　under　the　improved　method.