Alkali-activated　brick　powder　geopolymer　(BPG)　was　prepared　by　use　of　brick　powder　(BP)　under　the　activation　of　sodium　silicate-based　activator　with　silicate　modulus　of　1.6　and　alkali　dosages　of　2%,　4%,　6%,　8%,　and　the　effect　of　alkali　dosage　on　the　early　properties　and　reaction　mechanism　of　BPG　was　studied　in　this　paper.　Results　show　that　the　BPG　paste　prepared　with　alkali　dosage　of　6%　exhibits　the　best　fluidity　(180　mm).　With　increasing　alkali　dosage,　the　dissolution　rate　of　Al　from　BP　first　increases　and　then　decreases.　The　negative　correlation　exists　between　the　setting　time　of　BPG　and　the　dissolution　rate　of　Al　from　BP.　The　optimal　compressive　strength　reaches　31.1　MPa　at　the　alkali　dosage　of　6%　after　cured　for　3　days　(T　=　70?,　RH　=　30%).　Lower　or　excessive　alkali　dosage　is　both　unfavorable　to　the　enhancement　of　strength.　The　calorimetry,　FTIR　and　NMR　results　show　that　the　increase　in　alkali　dosage　(&　LE;6%　Na2O)　improves　the　reaction　degree,　promotes　the　formation　of　network　structures　and　increases　the　Al-rich　structural　units　(Q4(3Al)　and　Q4(4Al))　due　to　the　beneficial　effect　of　alkali　enhancement　on　dissolution　of　Al　from　BP,　thereby　increasing　the　polymerization　degree　of　reaction　products　and　enhancing　the　compressive　strength　of　BPG.　However,　the　higher　alkali　dosage　(8%　Na2O)　impedes　the　further　dissolution　of　Al　and　the　formation　of　Al-rich　structural　units,　which　results　in　the　lower　reaction　degree　and　compressive　strength.