Black stool in half a month after stoma surgery is mainly considered to be related to gastrointestinal bleeding, dietary influence and drug influence. 1. Bleeding from digestive tract: During stoma surgery, the digestive organs are damaged, resulting in bleeding from the digestive tract, which can lead to the phenomenon of black stools. 2. Dietary influences: consuming a lot of pig blood, duck blood and other iron-rich foods, or mulberry, black sesame and other foods that contain a lot of melanin can also lead to black stools. 3. Drug influence: recent consumption of ferrous sulfate or bismuth pectin and other drugs, will also affect the color of stool, and then the phenomenon of black stool. Ostomy surgery half a month out of black stool may also be other reasons, it is recommended to consult a doctor to confirm the diagnosis, and under the guidance of the doctor to deal with, so as not to delay the condition.