A　framework　of　the　non-orthogonal　elastoplastic　constitutive　model　for　unsaturated　soil,　which　takes　the　effective　degree　of　the　saturation　and　Bishop’s　effective　stress　as　the　basic　constitutive　variables,　is　presented　from　the　perspective　of　the　magnitude　and　direction　of　the　strain　increment.　The　non-orthogonal　plastic　flow　rule　is　adopted　to　directly　determine　the　direction　of　the　plastic　strain　increment　through　the　yield　function.　The　conundrum　of　constructing　the　plastic　potential　function　is　avoided.　In　the　context　of　the　proposed　framework,　a　non-orthogonal　elastoplastic　constitutive　model　of　unsaturated　soil　is　developed　by　determining　the　specific　yield　function,　hardening　parameter,　and　soil-water　characteristic　curve.　The　material　parameter　μ　is　incorporated　to　capture　the　mechanical　and　hydraulic　behavior　of　unsaturated　soil　with　different　stiffness.　All　material　parameters　have　clear　physical　meanings　and　can　be　calibrated　through　laboratory　tests.　The　mechanical　and　hydraulic　behavior　of　unsaturated　soil　with　different　stiffnesses　are　analyzed　through　two　classical　stress　paths,　i.e.,　the　conventional　triaxial-shearing　path　with　constant　suction　and　the　wetting　path　with　constant　net　stress.　The　superiority　of　the　proposed　model　was　verified　by　comparing　the　predicted　results　with　the　experimental　data　of　unsaturated　soil.　©　2022　Chinese　Academy　of　Sciences.　All　rights　reserved.