A　unified　displacement　function　of　the　cross-section　of　a　circular　shallow　tunnel,　expressed　by　the　Fourier　series,　is　proposed.　The　unified　displacement　function　can　reflect　main　deformation　behaviors　of　the　tunnel　cross-section.　Five　basic　deformation　modes　corresponding　to　the　expansion　order　n　=　2　show　the　horizontal　and　vertical　asymmetrical　deformation,　which　is　a　complete　deformation　mode.　This　complete　displacement　mode　is　implemented　into　the　complex　variable　solution　for　analytically　predicting　the　tunnelling-induced　ground　deformation.　The　effects　of　the　tunnel　cross-section　deforming　parameters　and　the　＂Buoyancy　effect＂　on　the　displacement　field　are　discussed.　Case　studies　from　the　section　MS-5　of　the　Docklands　Light　Railway　Lewisham　Extension　are　used　to　verify　the　capacity　and　applicability　of　the　proposed　solution.　The　presented　solution　provides　a　simplified　indication　for　evaluating　the　tunnel　deformation　under　complex　geological　and　construction　conditions.