In　this　paper,　we　employ　the　atomistic-continuum　method　to　open　a　new　way　to　precisely　measure　the　thickness　of　one-atomic　material.　The　wall　thickness　of　graphene　is　exactly　extracted　to　be　0.0739　nm　by　fitting　the　first　eight　natural　frequencies　of　a　series　of　simply-supported　graphene　using　atomistic-continuum　method　with　classical　plate　theory.　The　Young＇s　modulus　and　bending　rigidity　are　determined　to　be　3.1851　TPa　and　0.8066　eV.　By　using　this　thickness,　the　free　vibration　studies　of　clamped　case,　which　removes　the　effect　of　dangling　bonds,　by　the　atomistic-continuum　method,　molecular　mechanics　and　classical　plate　theory　are　found　to　be　in　a　good　agreement,　confirming　its　accuracy.　Inherited　it　to　the　hollow　tubular　structure,　it　is　found　that　both　Timoshenko　and　Euler-Bernoulli　beam　models　also　give　a　quite　close　prediction　of　carbon　nanotubes　as　compared　with　molecular　mechanics.　This　means　the　discrepancy　between　atomic　simulation　and　continuum　mechanics　is　no　other　than　the　unreal　wall　thickness.　Besides,　the　usage　of　scale　parameter　and　its　value　is　also　discussed.