Blood belongs to the connective tissue of the human body. The human body is divided into four major tissues according to the composition of cells, which are epithelial tissue, nerve tissue, muscle tissue and connective tissue, among which blood is a kind of connective tissue. Blood is a liquid composed of blood cells and plasma, which circulates continuously in the body’s blood vessels to deliver various nutrients to the body and perform important functions such as immunity. Blood is mainly composed of blood cells and plasma, of which blood cells include red blood cells, white blood cells and platelets, accounting for about 45% of the total blood composition, while plasma is composed of water and various clotting factors and antibodies, the composition is very complex, and plasma accounts for about 55% of the total blood composition. Blood is a very important connective tissue in the human body, and it plays an important physiological function for the normal functioning of the human body.