Coronary　artery　aneurysms　(CAAs)　have　been　reported　to　associate　with　an　increased　risk　for　thrombosis.　Distinct　to　the　brain　aneurysm,　which　can　cause　a　rupture,　CAA＇s　threat　is　more　about　its　potential　to　induce　thrombosis,　leading　to　myocardial　infarction.　Case　reports　suggest　that　thrombosis　risk　varied　with　the　different　CAA　diameters　and　hemodynamics　effects　(usually　wall　shear　stress　(WSS),　oscillatory　shear　index　(OSI),　and　relative　residence　time　(RRT))　may　relate　to　the　thrombosis　risk.　However,　currently,　due　to　the　rareness　of　the　disease,　there　is　limited　knowledge　of　the　hemodynamics　effects　of　CAA.　The　aim　of　the　study　was　to　estimate　the　relationship　between　hemodynamic　effects　and　different　diameters　of　CAAs.　Computational　fluid　dynamics　(CFD)　provides　a　noninvasive　means　of　hemodynamic　research.　Four　three-dimensional　models　were　constructed,　representing　coronary　arteries　with　a　normal　diameter　(1x)　and　CAAs　with　diameters　two　(2x),　three　(3x),　and　five　times　(5x)　that　of　the　normal　diameter.　A　lumped　parameter　model　(LPM)　which　can　capture　the　feature　of　coronary　blood　flow　supplied　the　boundary　conditions.　WSS　in　the　aneurysm　decreased　97.7%　apparently　from　3.51　Pa　(1x)　to　0.08　Pa　(5x).　OSI　and　RRT　in　the　aneurysm　were　increased　apparently　by　two　orders　of　magnitude　from　0.01　(1x)　to　0.30　(5x),　and　from　0.38　Pa-1　(1x)　to　51.59　Pa-1　(5x),　separately.　Changes　in　the　local　volume　of　the　CAA　resulted　in　dramatic　changes　in　local　hemodynamic　parameters.　The　findings　demonstrated　that　thrombosis　risk　increased　with　increasing　diameter　and　was　strongly　exacerbated　at　larger　diameters　of　CAA.　The　2x　model　exhibited　the　lowest　thrombosis　risk　among　the　models,　suggesting　the　low-damage　(medication)　treatment　may　work.　High-damage　(surgery)　treatment　may　need　to　be　considered　when　CAA　diameter　is　3　times　or　higher.　This　diameter　classification　method　may　be　a　good　example　for　constructing　a　more　complex　hemodynamic-based　risk　stratification　method　and　could　support　clinical　decision-making　in　the　assessment　of　CAA.