Aim To investigate the distribution characteristics of plasma low density lipoprotein (LDL) subfractions in patients with myocardial infarction and to analyze the correlation between the subfractions and serum clinical biochemical indicators in patients with acute myocardial infarction (AMI) and old myocardial infarction (OMI). MethodsThe fresh serum of 14 patients with acute myocardial infarction (AMI), 24 patients with old myocardial infarction (OMI) and 19 healthy subjects at the Second Affiliated Hospital of Dalian Medical University from June to December in 2015 were collected and screened. Plasma LDL subfractions composition and content were determined by Lipoprint subclass analysis system. Results Serum LDL average particle diameter, the content and percentage of I-LDL were significantly decreased (P＜0.01), and the content and percentage of S-LDL were significantly increased in acute myocardial infarction and old myocardial infarction (P＜0.01). From acute myocardial infarction to old myocardial infarction, serum S-LDL, especially correlation of LDL₅C, LDL₆C, LDL₇C and serum TC, LDLC, ApoB, CK-MB, cTnT had undergone significant changes. Conclusion Compared with LDLC concentration increase, the decrease of LDL particle size and the increase of S-LDL content and percentage were very important for the accurate detection and diagnosis of patients with clinical myocardial infarction. The correlation between serum LDL₅C, LDL₆C, LDL₇C and clinical biochemical indicators have great diagnostic value for the diagnosis of acute myocardial infarction and the differential diagnosis of acute myocardial infarction.