Al　has　significant　effect　on　properties　of　minerals.　We　reported　crystal　structure　and　elasticity　of　phase　H,　an　important　potential　water　reservoir　in　the　mantle,　which　contains　different　Al　using　first　principles　simulations　for　understanding　the　effect　of　Al　on　the　phase　H.　The　crystal　and　elastic　properties　of　Al　end-member　phase　H　(Al2O4H2)　are　very　different　fromMgend-member　(MgSiO4H2)　phaseHand　two　aluminous　phase　H　(Mg0.875Si0.875Al0.25O4H2　(12.5at%　Al)　and　Mg0.75Si0.75Al0.5O4H2　(25at%　Al)).　However　differences　between　Mg　end-member　phase　H　and　aluminous　phase　H　are　slight　except　for　the　O-H　bond　length　and　octahedron　volume.　Al　located　at　different　crystal　positions　(original　Mg　or　Si　position)　of　aluminous　phase　H　has　different　AlO6　octahedral　volumes.　For　three　Al-bearing　phase　H,　bulk　modulus　(K),　shear　modulus　(G),　compressional　wave　velocity　(Vp)　and　shear　wave　velocity　(Vs)　increase　with　increasing　Al　content.　Under　high　pressure,　density　of　phase　H　increases　with　increasing　Al　content.　The　Al　content　affects　the　symmetry　of　the　phase　H　and　then　affects　the　density　and　elastic　constants　of　phase　H.　The　total　ground　energy　of　phase　H　also　increases　with　increasing　Al　content.　So　an　energy　barrier　for　the　formation　of　solid　solution　of　phase　H　with　delta-phase　AlOOH　is　expected.　However,　if　the　phase　H　with　delta-phase　AlOOH　solid　solution　does　exit　in　the　mantle,　it　may　become　an　important　component　of　the　mantle　or　leads　to　a　low　velocity　layer　at　the　mantle.　(C)　2018　Author(s).