Blood is not a colloid, but is primarily a red, opaque, viscous liquid that flows through the body’s blood vessels and heart. Colloid, also known as gelatinous dispersion is a more homogeneous mixture, in the colloid contains two different states of matter, a dispersed phase, the other continuous phase. Part of the dispersed mass is composed of tiny particles or droplets, the dispersed mass particle diameter between 1~100nm of the dispersion system is colloidal. Blood is mainly composed of plasma and blood cells, the size of blood cells varies from a few micrometers to tens of micrometers, and plasma contains plasma proteins, electrolytes and so on. Therefore blood is a more complex mixture of components, while plasma is a mixed system of colloids and crystals together. Generally 1L of plasma will contain 900~910g of water, 65~85g of protein and 20g of low molecular material, low molecular material will also contain a variety of electrolytes and organic compounds. Blood cells include red blood cells, white blood cells and platelets, and their lifespan is 120 days, 9~13 days and 8~9 days respectively, and there are 40ml of blood cells dying of aging every day, and there are a corresponding number of new cells. In summary, blood is not a colloid, is a more complex mixture of components. Blood has important physiological functions, and if the total amount of blood decreases excessively or its composition changes abnormally, it may trigger serious consequences.