Objective To investigate the correlations of thromboelastography (TEG) maximum amplitude (MA) and platelet parameters with the 3-vessel lesions in the elderly patients with acute coronary syndrome (ACS). Methods A total of 129 elderly patients with ACS confirmed by coronary angiography admitted in the Center of Geriatrics of Lianyungang Clinical College from June 2018 to December 2020 were enrolled in this study. According to the number of involved coronary artery lesions, they were divided into 1- (n=34), 2- (n=41) and 3-vessel groups (n=54). The TEG (MA) and platelet parameters were compared among different groups. SPSS statistics 19.0 was used for statistical analysis. ANOVA analysis of variance, Chi-square test or Kruskall-Wallis test was applied for comparison among the groups, and Chi-square test or LSD test was employed for comparison between groups depending on date type. Multivariate logistic regression analysis was used to analyze the independent risk factors of 3-vessel disease. Results TEG (MA) level of the elderly patients in the 1-vessel group was significantly lower than that in the 2- and 3-vessel groups [(58.60±7.17) vs (61.41±7.44) and (62.07±6.50) mm, P<0.05]. The mean platelet volume (MPV) level of the ACS elderly patients was in a decreasing order from the 1-vessel group to the 2-vessel group and then the 3-vessel group [(9.37±1.21), (10.19±1.34) and (10.95±1.25) fL, P<0.05]. Multiple logistic regression analysis showed that age, TEG(MA), MPV, platelet count (PLT) and platelet hematocrit (PCT) were risk factors for 3-vessel lesions of coronary artery. Receiver operating characteristic curve analysis indicated that the sensitivity and specificity of TEG (MA) combined with MPV were 82.43% and 67.18%, respectively, in the prediction of 3-vessel lesions in the patients. In the high MPV group (n=78), the incidence of MACE was 17.9% and the all-cause mortality was 2.6% during hospital and in 3 months after discharge. While the incidence was 7.8%, and no death cases were found in the low MPV group (n=51), with statistical difference between the 2 groups (P<0.05). Conclusion MPV at admission is not only associated with, but also an independent risk factor for, and shows predictive value for 3-vessel lesions in elderly ACS patients. It is also correlated with the high incidence of MACE events in the patients during hospital and in 3 months after discharge. TEG(MA) at admission is associated with multivessel coronary artery disease in them.