In　accordance　with　the　collapse　characteristic　of　trench　wall　during　underground　diaphragm　wall　construction,　a　modified　three-dimensional　(3D)　failure　mechanism　of　trench　wall　is　established.　By　introducing　nonlinear　characteristic　and　the　nonhomogeneity　of　soil　into　the　theoretical　calculation,　the　objective　function　of　the　safety　factor　(F-s)　of　the　trench　wall　in　the　limit　condition　is　derived,　and　the　upper　bound　solution　of　the　F-s　of　the　slurry　trench　is　derived　by　employing　the　optimization　computation.　To　prove　the　validity　of　the　presented　approach,　the　solutions　derived　from　the　presented　method　are　compared　with　those　previous　solutions　and　the　comparing　results　show　a　good　agreement.　Moreover,　the　parametric　analysis　is　conducted　to　study　the　effect　of　various　parameters　on　the　stability　of　trench　wall.　The　results　of　parametric　analysis　show　that　nonlinear　and　the　nonhomogeneous　parameters　have　significant　influence　on　the　safety　factors,　and　the　nonlinear　failure　characteristic　of　the　nonhomogeneity　of　soil　cannot　be　ignored　in　the　practical　engineering.