Background:　When　the　coronary　artery　expands　more　than　two　times　its　diameter,　it　will　form　a　coronary　artery　aneurysm　(CAA).　CAA　can　lead　to　myocardial　ischemia.　In　this　paper,　the　mechanism　of　myocardial　ischemia　induced　by　CAA　was　studied　by　geometric　multiscale　method.　Methods:　Four　kinds　of　three-dimensional　models　of　CAA　with　different　dilation　diameters　were　established　on　the　basis　of　normal　three-dimensional　models.　The　dilation　diameters　were　2,　3,　5　and　7　times,　capacitance　was　added　after　the　CAA　to　simulate　the　elasticity　of　the　vascular　wall.　Results:　A　large　number　of　eddies　exist　in　CAA.　2-7　times　model:　1.1-14.4%　reduction　of　blood　flow　downstream　of　CAA　and　5,　7　times　model　showed　upstream　diastolic　backward　flow,　the　backward　flow　rate　was　1.1%　and　5.6%,　respectively.　The　aveWSS　at　the　CAA　was　1.76-0.35Pa;　the　relative　retention　time　was　1.1-14.6　Pa-1;　the　average　vorticity　was　0.0085-231.7s(-1).　Conclusion:　CAA　can　store　blood,　and　the　elasticity　of　the　wall　of　CAA　results　in　the　flow　of　blood　upstream.　These　two　reasons　make　the　downstream　flow　of　CAA　decrease　and　easily　form　intratumoral　thrombosis,　which　may　lead　to　myocardial　ischemia.