After having blood drawn, many people will experience bruising and swelling at the site of the blood draw. The reason for this phenomenon, most of them are caused by the incorrect pressing site after blood drawing, and some of them are caused by their own blood system diseases. Incorrect pressing site, many people just press the needle piercing skin after bleeding, which is incorrect, when pressing should be pressed on the upper side of the needle piercing skin, and press in the position of the needle piercing blood vessels, in order to effectively prevent bleeding and avoid bruising phenomenon. If the bruising occurs due to incorrect pressure, it can be treated by applying hot compresses, which can cause the bruising to be absorbed quickly. Another reason is that there are problems with the blood system, such as thrombocytopenia, coagulation disorders and other diseases. The diagnosis can be clarified through blood laboratory tests. This situation should be timely symptomatic treatment to avoid serious consequences.