Abstract: Objective To investigate the risk factors of subcutaneous hemorrhage caused by low molecular weight heparin in acute coronary syndrome patients and provide references for effective precaution. Methods Eighty adult patients who admitted to coronary care unit in General Hospital of Chinese People's Armed Police Forces from October 2014 to June 2015 were enrolled in this study. They were administered heparin subcutaneously, each patient received two injections in two ways. Way A: patients were injected for 10 s, and needles were pulled out after 10 s, the injection areas were pressed gently for 10 s; Way B: patients were injected for 10 s, and needles were pulled out after 10 s, the injection areas were pressed gently for 5 min. Injection areas were assessed for the presence of subcutaneous hemorrhage at 48 h after each injection and patients were divided into hemorrhage group and control group. Clinical data about patients were retrospectively analyzed, including age, gender, BMI, abdominal skinfold, diabetes history, using insulin, APTT, INR and platelet number. Univariate and multivariate Logistic regression analysis were conducted to compare the indicators mentioned above between the two groups to find out the risk factors. Results Hemorrhage group had 94 injections, and control group had 66 injections. Age, gender, diabetes history, using insulin, APTT, INR and platelet number were not significantly different between the two groups (P＞0.05); BMI, abdominal skinfold and pressing were significantly different between the two groups (P＜0.05). The multivariate Logistic regression analysis showed that pressing after injection was a risk factor (P＜0.05). Conclusion Patients with low BMI seem to be prone to have subcutaneous hemorrhage, but the degree of pressing (heavy strength, long time) is a risk factor of subcutaneous hemorrhage.