A　framework　of　the　plastic-damage　model　with　double　scalar　variables　is　established　in　nominal　stress　space　under　the　small　deformation　assumption.　In　the　damaged　part,　a　damage　tensor　composed　of　double　scalar　variables　is　presented　to　comprehensively　characterize　the　isotropic　damage　behavior　in　three-dimensional　(3D)　conditions.　The　damage　laws　of　Young＇s　modulus　and　shear　modulus　are　proposed　to　capture　their　different　damage　characteristic　observed　in　the　test.　For　one-dimensional　(1D)　and　3D　conditions,　the　applicability　of　single　scalar　and　double　scalar　damage　variables　is　discussed.　The　macroscopic　damage　difference　between　these　two　damage　variables　when　describing　damage　under　3D　conditions　is　analyzed.　In　the　plastic　part,　the　plastic　strain　increment　is　determined　by　two　parts　of　magnitude　and　direction.　The　magnitude　is　obtained　by　the　consistency　condition,　and　the　flow　direction　is　defined　by　the　nonorthogonal　flow　rule　that　can　satisfactorily　reproduce　the　dilatancy　behavior　of　concrete.　The　proposed　model　is　implemented　by　the　explicit　Runge-Kutta　(RK)　method　with　the　fifth-order　accuracy　and　the　Pegasus　method.　The　performance　of　the　model　is　assessed　by　the　comparison　results　between　the　model　and　the　cyclic　loading　and　unloading　test　data　under　different　stress　paths.