Aim To analyze the risk factors profile, clinical data, characteristics of coronary angiograph, laboratory characteristics and prognosis features in acute ST elevation myocardial infarction (STEMI) patients under 45 years old. Methods A cohort of 1 551 STEMI patients were divided into≤45-year old group (n＝120) and ＞45-year old group (n＝1 431). The baseline data, coronary angiography results, laboratory results, and in-hospital prognosis were compared between two groups. Results The percentages of males, smoking cigarettes, alcohol consumption were higher in ≤45-year old group than those in ＞45-year old group (P＜0.01), while the percentages of complications of diabetes, hypertension and stroke were lower in ≤45-year old group than those in ＞45-year old group (P≤0.01). The percentages of percutaneous coronary intervention was higher in ≤45-year old group than that in ＞45-year old group (P＜0.05), while the percentages of coronary artery bypass grafting (CABG) was lower in ≤45-year old group than that in ＞45-year old group (P＜0.05). Gensini scores were lower in ≤45-year old group than those in ＞45-year old group (P＜0.05). The levels of fasting blood glucose (FBG), high density liptein cholesterol (HDLC), blood urea nitrogen (BUN), high sensitive C-reactive protein (CRP), C-reactive protein toalbumin ratio (NLR) were lower in ≤45-year old group than those in ＞45-year old group (P＜0.05), while the levels of triglyceride (TG), total protein (TP), albumin (ALB), calcium(Ca), natrium(Na), white blood cell (WBC), lymphocyte (LYM), eosinophil (EO), red blood cell (RBC), hemoglobin (Hb), platelet (PLT), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT) were higher in ≤45-year old group than those in ＞45-year old group (P＜0.05). The days, the incidences of major adverse cardiovascular events(MACE) and all-cause death during hospital were lower in ≤45-year old group than those in ＞45-year old group (P＜0.05). In multivariate analysis, hypertension, smoking cigarettes, alcohol consumption and high NLR were independently associated with MACE during hospital in ≤45-year old group. Conclusion The risk factors profile such as males, smoking cigarettes, alcohol consumption were more obvious, and the percentages of hypertension is second only to smoking in ≤45-year old group. They also have relatively simple coronary artery disease, light inflammation response, the favorable prognosis.Our analysis suggests that hypertension, smoking cigarettes, alcohol consumption and high NLR are independently associated with MACE during hospital in ≤45-year old group.