Co-catalyst　engineering　has　significantly　bolstered　the　tunable　photoinduced　charge　migration/separation　in　solar-driven　photoelectrochemical　(PEC)　technology,　but　intricate　synthesis　procedures,　unfavorable　long-term　stability,　high　cost,　and　difficult　interface　configuration　modulation　retard　the　exploration　of　robust,　stable,　easily　accessible,　novel　and　highly　efficient　artificial　photosystems.　Herein,　we　conceptually　unravel　that　a　solid　non-conjugated　insulating　polymer　of　poly(allylamine　hydrochloride)　(PAH)　is　able　to　function　as　an　ideal　interfacial　co-catalyst　to　accelerate　the　charge　separation　of　metal　oxide　(MO)　substrates.　In　contrast　to　the　conventional　cognition　that　solid　non-conjugated　polymers　in　principle　cannot　participate　in　the　charge　transfer　process　owing　to　the　deficiency　of　delocalized　pi　electrons　along　the　molecular　framework,　we　have　ascertained　that　non-conjugated　PAH　layer-by-layer　self-assembled　on　the　MOs　effectively　enables　efficacious　extraction　of　holes　accumulating　on　the　MOs/(PAH)n　heterostructured　photoanodes　to　boost　solar　water　oxidation,　thereby　substantially　suppressing　the　charge　recombination　and　prolonging　the　charge　lifetime.　Moreover,　the　crucial　impacts　of　PAH　on　the　interfacial　charge　transport　kinetics,　efficiency,　and　mechanism　together　with　the　origin　of　insulating　polymer　mediated　carrier　trapping　sites　are　comprehensively　probed.　Our　work　would　attract　enduring　interest　in　exploring　insulating　polymer　co-catalysts　to　advance　solar　energy　conversion.