Stools with bad stomach may have changes in volume, color, smell, abnormal composition, etc. Specific diagnosis and treatment should be carried out under the guidance of a doctor. 1. Changes in volume: mostly manifested as diarrhea (i.e., increased frequency of defecation, increased fecal output), seen in patients with chronic gastritis, gastroesophageal reflux disease (GERD), gastro-colonic fistula, gastric cancer, and so on. 2. Color change: it mostly manifests as tar-colored feces (also known as black feces), which is seen in patients with gastric hemorrhage and can be caused by gastric ulcer, gastric smooth muscle tumor, erosive gastritis, gastric cancer and other diseases. 3. Odor changes: mostly manifested as ① malodorous odor: seen in patients with gastric hemorrhage; ② sour odor: seen in patients with functional gastric disease. 4. Abnormal composition changes: mostly manifested as (1) occult blood component: seen in patients with gastric bleeding; (2) hemoglobin crystal component: seen in patients with gastric bleeding. It should be noted that compared with lower gastrointestinal tract diseases, stomach diseases cause less abnormal fecal manifestations, therefore, clinically more upper gastrointestinal tract symptoms such as abdominal pain, nausea, vomiting, acid reflux and other symptoms as a hint of stomach diseases. However, all the above abnormal fecal changes must be timely medical treatment, under the guidance of the doctor for standardized diagnosis and treatment, do not blindly judge, dispose of their own, so as not to cause adverse consequences.