Integrating　two-dimensional　(2D)　ferroelectric　materials　into　van　der　Waals　(vdW)　heterostructures　for　photocatalytic　water　splitting　provides　new　opportunities　to　solve　the　energy　crisis　and　environmental　pollution.　However,　the　effect　of　polarization　reversal　in　the　ferroelectric　layer　of　ferroelectric-based　heterostructures　on　the　photocatalytic　mechanism　is　still　unclear.　Herein,　utilizing　density　functional　theory　alongside　non-adiabatic　molecular　dynamics　(NAMD)　simulations,　the　photocatalytic　mechanism　of　the　As/In2Se3　vdW　heterostructure　is　systematically　investigated.　The　NAMD　results　revealed　that　the　photo-generated　charge　carrier　transfer　pathway　of　the　As/In2Se3　heterostructure　follows　the　typical　type-II　pathway,　irrespective　of　the　polarization　states　of　the　In2Se3　layer.　The　ultrafast　interlayer　photo-generated　hole　transfer　in　As/In2Se3-P　up　arrow　and　electron　transfer　in　As/In2Se3-P　down　arrow　ensure　efficient　charge　transport,　thereby　enhancing　the　utilization　efficiency　of　carriers.　Interestingly,　by　adjusting　the　polarization　direction　of　the　In2Se3　layer,　the　As/In2Se3-P　up　arrow　and　As/In2Se3-P　down　arrow　can　be　employed　for　the　oxygen　evolution　reaction　(OER)　and　hydrogen　evolution　reaction　(HER),　respectively.　In　addition,　introducing　P　doping　can　significantly　reduce　the　overpotential　of　the　HER　using　As/In2Se3-P　down　arrow.　These　results　provide　a　new　insight　into　the　photo-generated　charge　carrier　transfer　pathway　of　2D　ferroelectric-based　vdW　heterostructures.