Blood color is related to the concentration of oxygen in the blood. The higher the concentration of oxygen, the color of blood is bright red; the lower the concentration of oxygen in blood, the blood is dark red. Therefore, if the blood is dark red in color, it means that the organism is in a state of oxygen deficiency, such as patients with chronic obstructive pulmonary disease and patients with cyanosis-type congenital heart disease. At this time, oxygen therapy should be given to improve the ventilation and air exchange function of the lungs, and for patients with cyanosis congenital heart disease, surgery can be performed. The dark color of blood, there is another possibility that it is caused by the increase of blood viscosity and slow blood flow, which is common in patients with particularly high blood sugar and high blood fat. At this time, it is necessary to go to the hospital for blood sugar and blood lipid tests. If the blood sugar is high, give treatment to lower sugar, if the blood fat is high, give treatment to lower fat.