We　have　analyzed　transverse　mode　characteristics　of　850-nm　oxide-confined　vertical-cavity　surface-emitting　laser　(VCSEL)　with　shallow　surface　relief　(SR)　structure　by　finite-difference　time-domain　(FDTD)　method.　We　have　used　FDTD　solution　software　to　complete　the　full　3D　simulations,　which　costs　us　about　24　hours　for　every　structure.　The　ring　form　SR　structure　has　been　located　in　the　central　of　the　topmost　DBR,　and　the　depth　is　1/4　optical　wavelength,　which　can　suppress　the　higher　mode　from　emitting　to　the　maximum　extent.　We　have　simulated　different　inner　diameter　of　the　ring　form　structures　on　10-mu　m　oxide-confined　VCSELs,　and　compared　the　transverse　mode　characteristics　with　that　of　ordinary　VCSEL.　Finally　find　the　structure　can　effectively　decrease　far-field　divergent　and　improve　transverse　mode　performance.　The　most　suitable　inner　diameter　is　6.5-mu　m,　and　the　full-width　half-maximum　of　the　far-field　divergent　angle　is　5.5　degrees,　which　provides　guideline　for　actual　device　fabrication.