Arterial blood is difficult to draw because of the following three reasons: 1. The location of arteries in the human body is well protected, so they are all in the depths, including within the deepest layers of the muscles, so it is difficult to find the arteries, and sometimes the arteries can be found, but the positioning is still inaccurate. 2. Arteries are very difficult to penetrate with a puncture needle because of the thicker and more elastic walls, and it takes a very long puncture needle and better skills to draw the blood. 3. It is difficult to stop bleeding after arterial blood extraction because of the high pressure inside the artery. In many cases, it is necessary to press for a long time to stop the blood without aneurysm.