As　typical　representatives　of　group　III　chalcogenides,　InSe,　α-In2Se3,　and　β′-In2Se3　have　drawn　considerable　interest　in　the　domain　of　photoelectrochemistry.　However,　the　microscopic　mechanisms　of　carrier　dynamics　in　these　systems　remain　largely　unexplored.　In　this　work,　we　first　reveal　that　hot　electrons　in　the　three　systems　have　different　cooling　rate　stages　and　long-lived　hot　electrons,　through　the　utilization　of　density　functional　theory　calculations　and　nonadiabatic　molecular　dynamics　simulations.　Furthermore,　the　ferroelectric　polarization　of　α-In2Se3　weakens　the　nonadiabatic　coupling　of　the　nonradioactive　recombination,　successfully　competing　with　the　narrow　bandgap　and　slow　dephasing　process,　and　achieving　both　high　optical　absorption　efficiency　and　long　carrier　lifetime.　In　addition,　we　demonstrate　that　the　ferroelectric　polarization　of　α-In2Se3　not　only　enables　the　formation　of　the　double　type-II　band　alignment　in　the　InSe/α-In2Se3/InSe　heterostructure,　with　the　top　and　bottom　InSe　sublayers　acting　as　acceptors　and　donors,　respectively,　but　also　eliminates　the　hindrance　of　the　built-in　electric　field　at　the　interface,　facilitating　an　ultrafast　interlayer　carrier　transfer　in　the　heterojunction.　This　work　establishes　an　atomic　mechanism　of　carrier　dynamics　in　InSe,　α-In2Se3,　and　β′-In2Se3　and　the　regulatory　role　of　the　ferroelectric　polarization　on　the　charge　carrier　dynamics,　providing　a　guideline　for　the　design　of　photoelectronic　materials.　©　2024　Author(s).