It has been confirmed in a study of 120 patients that the subcutaneous injection of heparin sodium (authentic low-molecular weight heparin) was performed by slow injection with the injection time of 30s and 10s, respectively. The results showed that the injection time of 30s was associated with a reduced incidence of subcutaneous hemorrhage and a reduced mean ecchymosis diameter. Its basis is: when slowly injecting the drug, the drug solution in the subcutaneous production of small tension, should avoid the subcutaneous tension should be too large and the drug solution by puncture hole overflow, so the incidence of bleeding is low.