Gastrointestinal bleeding is a relatively common clinical presentation, and there are many diseases that can cause it. The amount of bleeding can be judged by looking at changes in blood count, but also by the color of the stool to infer first love. How can we see the amount of bleeding by the color of the stool? The general statement is that when the amount of gastrointestinal bleeding in 1 day is more than 5 ml, the stool can be positive for occult blood, while the stool color can be unchanged at this time. However, when the amount of bleeding reaches 50-70 ml, the stool can be black. Further, if there is a dark tarry stool or dark red stool, the amount of bleeding is about 100-500 ml; if the tarry stool lasts for 2-3 days, the amount of bleeding is at least 1000 ml; the fecal occult blood test can be strongly positive at this time.