Preoperative radiotherapy for rectal cancer usually lasts for 2~4 courses for about 25 days, and the specific course of treatment should be decided according to the patient’s pathological staging and clinical staging. The treatment of rectal cancer mainly adopts a comprehensive individualized treatment plan combining radiotherapy and surgery. Preoperative radiotherapy for rectal cancer can eliminate or inhibit local tumor primary foci and metastatic foci through radiation, which facilitates subsequent surgical resection, improves the success rate of surgery and reduces recurrence. Preoperative radiotherapy for rectal cancer can be divided into short time radiotherapy and long time radiotherapy. Short time radiotherapy is usually 1 course of radiotherapy, requiring 5 times of radiotherapy, which is applicable to early non-metastatic rectal cancer; long time radiotherapy is usually about 4 courses of radiotherapy, requiring 25 times of radiotherapy, which is applicable to middle and late rectal cancer, increasing the chance of surgical residual anal sphincter. Preoperative radiotherapy for rectal cancer should be standardized under doctors’ guidance, and all relevant indexes should be carefully monitored during radiotherapy to avoid adverse reactions.