Stomach pain and black stools cannot be diagnosed as malignant cancer, but malignant cancers and other lesions of the lower gastrointestinal system can present with black stools. The reason for the formation of black stool is that a small amount of bleeding stays in the gastrointestinal tract, and due to a longer period of time, it will form acidified ferroportin with hormones and enzymes in the gastrointestinal tract, and this substance can turn into a brown slag-like substance after staying in the gastrointestinal tract, and then it will become black stool when it is discharged from the body. The common cause of black stool is the malignant tumor of the lower gastrointestinal tract, which mainly takes black stool, coffee-colored stool or fresh blood stool as the main cause, such as the malignant tumor of the rectum, the malignant tumor of the sigmoid colon, and the lesion of the biliary tract, pancreas and duodenum will also have a certain chance to appear black stool. Therefore, if you have black stools with abdominal pain, it is recommended to go to a regular hospital to do a checkup, check the abdominal ultrasound, CT or other electronic gastroscopy and a series of tests.