There are several reasons for the bitterness of the mouth at night: First, it is a long time subhealth state, including lack of sleep, overwork, prolonged alcoholism, smoking, etc., will lead to the human mouth will appear bitter at night. Second, mostly seen in oral diseases, mostly seen in the oral micro-ecological imbalance, bacteria in the oral cavity and a large number of breeding and appear too thick tongue, bad breath, bitter mouth, mouth ulcers, etc.. Third, liver and gallbladder diseases, more common is cholecystitis, gallstones and chronic diseases of the liver, etc., can lead to bitterness of the mouth. Fourth, digestive system diseases. Mostly seen in gastric diseases, especially prolonged gastric ulcer, gastritis, etc., resulting in food indigestion and decay, with bitter mouth performance.