Rectal cancer usually has no special precursor manifestation, and there are no obvious symptoms in early stage. When the disease progresses, there will be changes in defecation habit, blood in stool and other manifestations. Rectal cancer is a malignant tumor originated from mucosal epithelium of rectum, the cause of which is unknown and may be related to factors such as environment, heredity, diet and life habits, etc. 40-80 years old is the high incidence age group, male is higher than female, urban is higher than rural, generally early symptoms are not obvious, so there is no precursor symptom performance. However, when there are frequent bowel movements, change of bowel habit, blood on the surface of stool, pain in lower abdomen, etc., one should go to the hospital for examination in time, which can be diagnosed by rectal finger test, endoscopy, laboratory examination or local sampling and pathological examination. Early detection, early diagnosis and early treatment of rectal cancer will improve the survival period and quality of life of patients. It is recommended that those with family history of rectal cancer and above 40 years old should do routine physical examination by colonoscopy, and pay attention to regular rechecking in daily life to monitor the changes of symptoms, and see the doctor in time for the appearance of uncomfortable symptoms. At the same time, we should adjust our dietary habits, eat more high quality protein food, increase the intake of fresh vegetables and fruits, avoid greasy and fried food, avoid smoking, alcohol and spicy stimulating food, etc., and prevent the occurrence of constipation and diarrhea. In short, some diseases have no precursor, to prevent in advance, in addition to personal protection to improve, be sure to do routine checkups, and more consultation with a professional doctor.