Stools that are thick and then become thin may be caused by normal physiological conditions or diseases. 1. Normal physiological situation: human stools are usually formed or soft stools, but the overall shape is more uniform, in the gastrointestinal discomfort, the habit of holding back the urge to delay defecation of the crowd, there may be dry stools caused by the appearance of the first thick and then thin shape, due to dry stools will come out of the first thick, but the second half of the intestinal tract after the softening of the water will become thin. 2. Non-physiological phenomenon: caused by certain diseases, such as colorectal tumors, pelvic tumors and so on, have a compression effect on the intestinal tract. In the lesion area, the stool will become thinner in shape when passing through the narrow area, and then it is recommended to improve the CT examination of abdomen and pelvis to make it clear. Therefore, the specific situation should be analyzed according to the clinical manifestations and physical condition, and should go to the regular hospital to avoid delaying the condition.