The black and yellow tongue coating may be caused by heat and injury to fluid, fluid deficiency and heat stagnation. However, the exact cause needs to be decided in conjunction with the patient’s other symptoms. In addition to black and yellow tongue coating, patients with heat injury may also have fever, thirst and desire to drink, dry and shriveled skin, sunken eyes, short and yellow urine, and dry and knotty stools, among other symptoms. In patients with deficiency of fluid and heat, in addition to black and yellow tongue coating, there may also be fever and thirst, dry lips and tongue, restlessness, dysuria, constipation, etc. If the symptoms are prolonged for a long period of time, there may also be fever, thirst and desire to drink, dry skin, sunken eyes, short and yellow urine and constipation. If the symptoms of black and yellow tongue coating are not relieved for a long time or accompanied by other discomforts, consult a doctor in time to identify the cause and carry out targeted treatment.