The subcutaneous injection area on the arm is usually located at the lower edge of the deltoid muscle. The lower edge of the deltoid muscle, the subcutaneous tissue is thicker, the injection is not easy to enter the muscle layer, so usually the lower edge of the deltoid muscle, used for the injection of various types of vaccines, but also easy to observe and select. Subcutaneous injection belongs to a common clinical way of drug delivery, mainly used for the injection of various vaccines, as well as insulin, low molecular heparin sodium and other drugs, often choose the lower edge of the deltoid muscle of the lateral upper arm. Before injecting drugs, the skin should be routinely sterilized, and during the injection process, the needle should be inserted and withdrawn quickly, and the pushing process should be slow, so as to reduce the patient’s pain. For subcutaneous injections, the drug should be administered by a medical professional and should not be abused on its own.