Dehydroxylation　of　biomass-based　platform　molecules　is　critical　for　obtaining　building　blocks　for　use　in　the　chemical　industry.　Acid　catalytic　dehydration　has　provided　a　feasible　route.　However,　simultaneously　pursuing　high　product-selective　and　ultra-stable　catalysts　for　the　dehydroxylation　of　polyols　remains　an　open　challenge.　In　this　study,　a　strategy　for　in-situ　Bronsted　acid　sites　(BAS)　with　chemo-adsorption　selectivity　is　proposed.　The　construction　of　defect　sites　B[3]　and　P[4]　species　has　been　proved　to　be　a　prerequisite　for　the　dynamic　acid　site　formation　at　hydrothermal　conditions.　The　BPO4　catalyst　with　in-situ　BAS　can　achieve　the　high　selectivity　of　acrolein　(similar　to　80%)　and　robust　stability　of　catalyst　(over　425　h)　using　glycerol　dehydration　as　a　model　reaction.　In　addition,　in-situ　BAS　is　highly　selective　for　secondary　hydroxyl　groups　and　has　been　extended　to　other　substrate　applications.　This　catalytic　strategy　provides　a　green,　efficient,　and　economical　approach　for　converting　biomassderived　polyols　to　high-value-added　chemicals.