Designing　Z-scheme　van　der　Waals　(vdW)　heterostructured　photocatalysts　is　a　promising　strategy　for　developing　highly　efficient　overall　water　splitting.　Herein,　by　employing　density　functional　theory　calculations,　we　systematically　investigated　the　stability,　electronic　structures,　photocatalytic　and　optical　properties　of　Al2SeTe,　GaSe,　and　InS　monolayers　and　their　corresponding　vdW　heterostructures.　Interestingly,　electronic　structures　show　that　all　vdW　heterostructures　have　direct　band　gaps,　which　is　conducive　to　the　transition　of　electrons　from　the　valence　band　to　the　conduction　band.　Notably,　Al2TeSe/GaSe　and　Al2TeSe/InS　vdW　heterostructures　possess　large　overpotentials　for　Z-scheme　photocatalytic　water　splitting,　as　proved　by　the　results　of　band　edge　positions　and　band　structure　bending.　Moreover,　these　vdW　heterostructures　exhibit　good　optical　absorption　in　ultraviolet　and　visible　light　regions.　We　believe　that　our　findings　will　open　a　new　avenue　for　the　modulation　and　development　of　Al2TeSe/GaSe　and　Al2TeSe/InS　vdW　heterostructures　for　photocatalytic　water　splitting.