S-gear　is　a　new　type　of　gear　with　the　advantages　of　small　sliding　coefficient,　high　meshing　efficiency　and　large　load-bearing　capacity　due　to　the　concave-convex　contact　in　a　vicinity　of　the　meshing　start　and　end.　In　view　of　the　excellent　characteristics　and　potential　value　of　S-gears,　this　paper　deeply　studies　the　designation　and　meshing　characteristics　of　the　S-gears.　First,　based　on　the　relationship　of　S-shaped　rack-cutter　and　machining　motion,　the　tooth　surface　of　the　S-gears　is　generated.　Second,　by　superimposing　the　surface　of　modified　volume　with　the　standard　tooth　surface,　the　modified　tooth　surface　of　S-gears　is　constructed.　On　this　basis,　using　MATLAB　programming,　the　coordinates　of　3D　grid　node　of　modified　S-gears　are　calculated.　Third,　loaded　tooth　contact　analysis　(LTCA)　is　used　to　study　the　meshing　characteristics　of　the　S-gears　with　longitudinal　modifications　and　misalignment　angle　errors.　Ultimately,　one　example　is　presented　and　the　result　shows　that　after　tooth　surface　modification,　the　load　distribution　of　S-gears　is　effectively　improved　and　error　sensitivity　is　greatly　reduced.　S-gear　is　a　new　type　of　gear　which　is　different　from　involute　gears　and　has　great　potential　application　prospect　in　large　load-bearing　field,　which　will　be　further　studied　in　the　future.　©　Published　under　licence　by　IOP　Publishing　Ltd.