Rectal cancer is mainly categorized according to morphology and cytology, and according to different categorization methods, rectal cancer will be divided into different types. 1. Morphological classification: rectal cancer is categorized by imaging and endoscopic examination, and according to the condition of the lesion and its relationship with the surrounding intestinal wall, it is classified into bulging type (the mass protrudes into the lumen), ulcerative type (necrosis of the intestinal wall), invasive type (rigidity of the intestinal wall) and so on. 2. Cytologic classification: according to the pathological examination results of cells, it can be distinguished, mainly including adenocarcinoma (the best), undifferentiated carcinoma, adenosquamous carcinoma, squamous carcinoma and so on. Through the classification of rectal cancer, the degree of malignancy and prognosis of rectal cancer can be differentiated, and combined with clinical TNM staging, standardized treatment can be carried out under the guidance of clinicians.