Stomach pain after radiotherapy for rectal cancer may be caused by stress ulcer and indigestion. 1. Stress ulcer: Radiotherapy for rectal cancer patients will put the organism in a state of stress, at this time, the gastrointestinal mucous membrane barrier of patients will be broken. Patients will not only have the symptoms of stomach pain, but also with acid reflux, abdominal distension, vomiting blood, black stool and so on. 2. Dyspepsia: some rectal cancer patients will feel anxious and nervous during radiotherapy, which may induce dyspepsia. The patients will have postprandial fullness, burning sensation in the middle and upper abdomen, early satiety, etc. It is recommended that rectal cancer patients should have a good digestion after radiotherapy. It is suggested that rectal cancer patients who have stomach pain after radiotherapy need to seek medical treatment in time, and doctors will choose appropriate measures for treatment according to the cause.