Tai　chi　culture　has　a　widespread　influence　on　the　world.　Tai-chi　diagrams,　as　the　symbol　of　Tai　chi　culture,　express　the　balance　between　Yin　and　Yang　through　the　centrosymmetric　pattern,　but　the　balance　connotation　of　Tai-chi　diagrams　needs　a　comprehensive　understanding　in　more　aspects,　e.g.,　the　balance　in　mechanics.　In　this　work,　we　propose　a　mechanics　theory　to　investigate　the　intrinsic　mechanism　of　Yin-Yang　equilibrium　in　ancient　and　modern　Tai-chi　diagrams.　The　model　based　on　the　minimum　potential　energy　theory　can　effectively　describe　the　interface　curves　of　the　Yin-Yang　equilibrium　by　modifying　boundary　conditions,　which　is　proven　by　experiments.　The　results　show　that　the　balance　of　Tai-chi　diagrams　is　not　only　manifested　in　its　symmetrical　appearance　but　also　reflected　in　its　intrinsic　balance　configuration　in　mechanics.　The　model　presented　herein　provides　a　new　perspective　to　understand　the　balance　of　Tai-chi　diagrams,　which　may　provide　useful　insights　into　the　applications　of　Tai-chi　diagrams.　©　2024　Author(s).