The causes of black tongue veins include physiological and pathological, and the pathological ones are mostly caused by thin mucous membrane and non-circulation of blood. 1. Physiological factors: the blackening of the base of the tongue may be the position of the tongue belly mucosa is too thin, resulting in the body of the base of the tongue veins through the color of venous blood, so it leads to the base of the tongue veins were dark red, looks relatively black, this is generally a normal physiological phenomenon. 2. Pathological factors: (1) The reason for the blackening of the base of the tongue is mostly due to the malformation of the blood vessels at the base of the tongue, which causes the blood vessels at the base of the tongue to be exposed gradually, resulting in the accumulation of blood in the location of the blue veins, and finally the blackening of the base of the tongue. (2) Black tongue tendon is very likely to be the emergence of blood circulation, caused by the bottom of the tongue bruises, and over time there will be black tongue tendon. Just a symptom can not determine the disease, it is recommended that the patient exclude physiological factors, timely consultation, identify the causes, targeted treatment.