Blood stasis is the accumulation of blood in the body, or blood that is blocked in the meridians and viscera by poor blood flow. Stasis of blood is a pathological product and a causative factor of certain diseases. The causes include Qi deficiency, Qi stagnation, blood cold, blood heat, all of which can cause blood to flow poorly, and trauma can also cause stasis of blood. The clinical manifestations of stasis of blood include pain, which is characterized by needling, and has a fixed location, refusal to press, which means that it does not like to press, and especially strong pain at night; lumps, which are on the surface of the body and are blue and purple in color. In the abdomen, it can be manifested as a lump; recurrent bleeding, blood in the stool, and on the skin as purple spots on the skin, spider red or bruises in the abdomen and varicose veins in the lower limbs. In women, it manifests as scanty menstruation, purple darkness, blood clots, and even amenorrhea; in the tongue it manifests as purple darkness, thin and astringent pulse, and knotted generation. The formation of blood stasis is related to Qi deficiency and Qi stagnation and blood cold causing blood stasis. Heat can also cause stasis, and can form clots when tormented by heat.