Venous blood collection is preferred from the veins in the arm area, i.e., the arm is tied, but the back of the hand, the inner ankle, and the femoral vein are also selected for blood collection in some special cases. Venous blood collection refers to the collection of venous blood for testing, usually from superficial veins. Superficial veins include the veins of the elbow, the back of the hand, the internal ankle vein, the femoral vein, and the external jugular vein. In general, adults prefer to collect blood from the median elbow vein of the elbow, while the cephalic vein and the vital vein can also be used when the median elbow vein is not suitable for puncture. Some children, infants and young children, the elbow vein is not obvious, it is difficult to puncture can also choose the scalp part of the more obvious vein puncture; some blood loss of the critically ill, the hand, elbow vein collapse, you can choose the femoral vein for blood collection by puncture. Venous blood collection can be performed in multiple sites, and it is necessary to choose the site of blood collection by puncture according to the patient’s venous condition.