The　strength　properties　of　transversely　isotropic　soils　are　closely　related　to　the　loading　direction.　These　direction-dependent　properties　have　been　testified　by　a　series　of　laboratory　tests.　Two　primary　features　for　peak　strength　are　obtained:　the　distortion　of　the　strength　curve　on　the　deviatoric　plane　and　the　change　of　the　internal　friction　angle　associated　with　the　direction　angle　between　the　major　principal　stress-acting　plane　and　the　depositional　plane.　How　to　describe　these　two　features　in　a　unified　way　is　a　difficult　and　hot　research　topic.　This　paper　aims　at　solving　this　problem　by　proposing　a　strength　parameter　that　was　obtained　by　projecting　the　microstructure　tensor　on　the　direction　of　the　spatial　mobilized　plane.　It　is　an　approach　to　extend　an　isotropic　strength　criterion　into　a　transverse　isotropy　one.　The　combination　of　the　proposed　strength　parameter　with　the　isotropic　non-linear　unified　strength　criterion　can　well　capture　the　distorted　strength　curve　and　its　evolution　with　the　increase　of　direction　angle.　The　effects　of　the　intermediated　principle　stress　ratio　b　and　the　direction　angle　S　are　also　analysed.　Material　parameters　in　the　proposed　criterion　can　be　conveniently　obtained　from　the　conventional　laboratory　tests.　It　is　demonstrated　that　the　new　proposed　criterion　can　be　verified　favorably　by　the　test　results.