Aim To delineate the plaque morphologic characteristics among stable angina pectoris(SAP) and acute coronary syndrome(ACS) by intravascular ultrasound(IVUS).Method 51 SAP patients with 63 vessels were recruited and 32 ACS patients with 46 vessels were checked by IVUS.Plaques were divided into soft,fibrous,calcified.The IVUS results of plaque compositions detection were compared between SAP and ACS.Results The ration of soft plaque,extent of remodeling index,external elastic membrane area(EEMA),plaque burden(PB),plaque rupture increased in ACS group.Thrombosis detection rate were not statisticly different between two groups.Conclusion The criteria of soft plaque located in the proximal part of main coronary branches or any detected soft plaque with positive remodeling index and minimal lumen area≤4 mm2 predicted the vulnerable plaque in ACS and deserved the aggressive treatment.