Blood in the stool is one of the common symptoms in patients with sigmoid colon cancer, but there is no correlation with the cancer stage. At present, the most commonly used clinical staging of sigmoid colon cancer is TNM staging. Sigmoid colon cancer is very easy to form erosions or even ulcers, and then the tumor ruptures and bleeds, causing blood in stool, which is one of the frequent symptoms of patients with intestinal cancer, and it can occur in all periods of the tumor, so the tumor staging cannot be inferred from the blood in stool. The current staging standard of sigmoid colon cancer is TNM staging, T refers to primary tumor, the deeper the tumor infiltration, the later the T staging; N refers to regional lymph node metastasis, the more local lymph node metastasis, the later the N staging; M refers to metastasis of distant organs, the emergence of metastasis of distant organs will be the M1 stage, i.e., the tumor is at an advanced stage. Different TNM combinations can lead to different clinical stages. If blood in stool is found in sigmoid colon cancer, it is suggested that patients should go to hospital as early as possible to improve relevant examinations and tests such as colonoscopy, chest and abdominal CT, tumor markers, bone scan, etc., so as to ask professional doctors to evaluate the clinical staging and then formulate the next step of treatment plan.