Hard stool before and thin stool after is related to constipation, intestinal occupational lesions, gastrointestinal dysfunction and other reasons, as follows. 1. Constipation: constipated patients due to excreta in the intestinal tract of water absorption is different, in the anal canal, rectal area of the accumulation of a long time will appear in the dry stool, while the back of the stool in the intestinal tube to stay a short period of time, the stool is more thin and soft. By eating more vegetables and fruits, eating a light diet, oral medication can help to improve the symptoms. 2. Intestinal space-occupying lesions: including intestinal polyps, intestinal cancer, etc. Not only will the stool be hard in the front and thin in the back, it may be accompanied with symptoms such as change of stool habit, mucous pus and blood stools, abdominal pain, anal swelling and other symptoms. 3. Gastrointestinal dysfunction: Gastrointestinal dysfunction can cause incoordination of gastrointestinal peristalsis, and the feces can not be fully digested and absorbed in the intestinal tract, which leads to hard and thin stools. There are many other causes of hard and thin stools, so it is recommended to consult a doctor for a clear diagnosis in order to avoid delaying the condition.