The　stabilized　soil　strength　of　compound　soft　soil　stabilizer,　which　is　composed　of　cementitous　component　and　expansible　component,　may　be　increased　significantly,　but　also　may　be　reduced.　The　causes　for　different　stabilization　effects　are　studied.　Three　compound　stabilizers　are　used　to　stabilize　two　soil　samples.　The　unconfined　compressive　strength　is　tested,　and　the　generation　rate　of　calcium　silicate　hydrate　CSH　and　ettringite　AFt　are　tested　by　XRD　tests　and　DSC-TG　tests.　The　results　show　that　the　stabilization　effect　of　compound　stabilizer　depends　on　the　coordination　between　AFt　generation　rate　and　CSH　generation　rate.　If　CSH　generation　quantity　is　still　little　and　the　cementitous　structure　is　very　weak　when　AFt　is　generated,　the　volume　expansion　caused　by　the　AFt　generation　process　will　increase　the　stabilized　soil　strength;　and　vice　versa.