Given　that　the　deformation　of　the　timber　is　susceptible　to　the　change　of　ambient　temperature　and　the　humidity,　a　timber　constitutive　model　that　can　accurately　describe　the　interaction　with　load　and　long-term　ambient　environment　was　proposed.　Firstly,　based　on　the　Tsai-Wu　yield　criterion,　the　Drucker　postulation　and　the　consistency　rule,　a　timber　constitute　model　considering　the　normal　creep　and　the　mechanical　absorption　creep　was　proposed.　Then,　the　deduced　constitutive　model　was　compiled　into　the　UMAT　subroutine　and　was　embedded　in　the　ABAQUS　software　by　using　the　Fortran　language,　which　realized　the　simulation　analysis　of　the　timber　characteristics　under　the　combined　action　of　load　and　ambient　environment.　Finally,　uniaxial　material　tests　and　mechanical　absorption　creep　tests　were　conducted　on　old　timber　to　verify　the　validity　of　the　proposed　constitutive　model.　Besides,　the　Hankinson　theorem　formula　was　also　employed　to　verify　the　validity　of　the　constitutive　model　when　the　timber　was　under　the　stress　in　perpendicular-to-wood-grain　direction.　The　results　show　that　the　errors　of　the　prediction　of　the　yield　stress　when　the　timber　is　subjected　to　longitudinal,　radial　and　chordwise　compressions　are　19.　5%,　4.　6%　and　8.7%,　respectively,　which　indicates　that　the　deduced　constitutive　model　and　the　user　subroutine　(UMAT)　are　effective　to　simulate　mechanical　properties　of　timber　under　the　uniaxial　and　the　perpendicular-to-wood-grain　direction　loading.　Moreover,　the　results　from　the　mechanical　absorption　creep　experiments　are　in　good　agreement　with　the　simulation　results,　which　means　that　the　deduced　constitutive　model　can　better　predict　the　timber　mechanical　behavior　under　the　combined　action　of　load　and　ambient　environment.　©　2021,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.