Based　on　the　results　of　test　under　complex　stress,　the　relationship　of　stress-strain　under　the　principal　stress　with　different　directions　is　studied　through　experiments,　and　according　to　this,　combined　with　the　concept　of　state,　an　elasto-plastic　constitutive　model　based　on　relationship　of　stress-dilatancy　and　simulated　hyperbolic　relationship　of　stress-strain　is　put　forward.　The　effect　of　direction　of　the　principal　stress　on　the　effective　stress　path　and　the　evolution　mode　of　stress-strain　is　described　by　use　of　simulated　hyperbolic　relationship　of　stress-strain.　The　experimental　parameters　are　determined　by　conventional　triaxial　tests.　It　is　shown　by　comparison　between　the　calculated　and　measured　results　that　introducing　the　state　parameters　based　on　the　concept　of　state　and　using　the　effect　of　the　direction　of　principal　stress　on　the　plastic　modulus,　the　effect　of　the　initial　physical　state　and　initial　anisotropy　on　the　stress-strain　relationship　of　sand　can　be　described.