Objective：To investigate the clinicopathological features，immunophenotype，and molecular genetic changes of switch/ sucrose non - fermentable complex（SWI/SNF）complex deficient carcinoma in digestive system，and to analyze the diagnosis and differential diagnosis points. Methods：The clinical data of 31 patients with SWI/SNF complex deficient carcinoma of digestive system were collected. The histological morphology was observed，and the immunohistochemical results and molecular alteration characteristics were summarized. Relevant literature was reviewed for analysis. Results：Among the 31 patients，19 were male and 12 were female，aged from 43 to 80 years，with a median age of 66 years. Location of disease：lower esophagus（gastroesophageal junction） 1 case，stomach 7 cases，right colon 3 cases，pancreas 18 cases，ampulla 2 cases. The maximum diameter of the lesions ranged from 1.5 to 18.0 cm（median，3.5 cm）. Histologically，15 tumors showed the morphology of undifferentiated carcinoma，and 16 were low - to moderately differentiated pancreatic ductal adenocarcinoma，adenosquamous carcinoma，or intraductal papillary mucinous neoplasm （IPMN）with associated invasive carcinoma. Immunophenotype：14 of the 15 undifferentiated carcinomas showed loss of BRG1 expression，and 1 pancreatic undifferentiated carcinoma showed partial loss of INI1 expression while retaining BRG1 expression；4 cases showed negative or only scattered expression of CK - pan in tumor cells，and other epithelial markers were positive in only individual tumor cells or mostly negative；7 cases showed weak to moderate positivity of Syn in some tumor cells，among which 2 cases showed scattered weak positivity of CD56 or INSM1 respectively，and all were negative for CgA. BRG1 expression was retained in 16 pancreatic/ampullary cancers，8 cases showed partial loss or reduced expression of INI1，and 8 cases retained expression；molecular pathology showed that 14 cases had SMARCB1 gene mutations，2 cases had SMARCA4 gene mutations，KRAS gene mutations were seen in all cases，and 14 cases had TP53 gene mutations. Conclusion：Some SWI/SNF complex deficient carcinomas in the digestive system are undifferentiated carcinomas without specific differentiation characteristics. Extragastrointestinal SWI/SNF complex deficient carcinoma may have more differentiated adenocarcinoma morphology. Detection of SWI/SNF proteins such as BRG1 and INI1 is recommended to reduce missed diagnosis and misdiagnoses. SWI/SNF - related gene mutations in pancreatic cancer are correlated with KRAS and TP53 gene mutations.