Expansive　soil　is　widely　distributed　and　often　needs　to　be　improved　for　engineering　and　construction　needs.　Using　blast　furnace　slag　and　fly　ash　as　precursors　and　NaOH　as　an　alkali　activator,　a　geopolymer　was　prepared　to　solidify　expansive　soil,　and　the　effect　of　nano-SiO2　on　the　compressive　strength　and　water　stability　of　the　geopolymer-solidified　expansive　soil　was　further　studied.　The　effects　of　alkali　addition　ratio,　nano-SiO2　addition　ratio,　and　curing　agent　addition　ratio　on　the　unconfined　compressive　strength　and　water　stability　of　the　cured　soil　were　studied　through　unconfined　compressive　strength　tests,　and　the　curing　mechanism　was　analyzed　by　electron　microscopy　scanning.　The　experimental　results　showed　that　the　unconfined　compressive　strength　and　water　stability　of　geopolymer-stabilized　soil　first　increased　and　then　decreased　with　an　increase　in　alkali　activator　dosage.　The　optimal　dosage　of　alkali　activator　was　found　to　be　12.5%.　Furthermore,　it　was　found　that　adding　nano-SiO2　can　further　enhance　the　strength　and　water　stability　of　solidified　soil.　When　the　content　of　nano-SiO2　was　3%,　the　unconfined　compressive　strength　was　increased　by　15%.　With　an　increase　in　the　content　of　nano-SiO2　doped　polymer　(GFNS),　the　unconfined　compressive　strength　and　water　stability　of　the　solidified　soil　showed　a　trend　of　first　increasing　and　then　decreasing,　reaching　a　peak　at　a　content　of　20%.　The　cementitious　materials,　such　as　hydrated　calcium　silicate　and　hydrated　calcium　silicate　aluminate,　generated　by　the　reaction　between　nano-SiO2　and　geopolymer　played　a　role　in　bonding　and　filling　in　the　solidified　soil.　Under　the　joint　action　of　the　two,　the　structural　arrangement　between　the　solidified　soil　particles　became　more　compact,　which　improved　the　strength　of　the　solidified　soil.