Objective To discuss CT manifestations of peritoneum lesion due to gastrointestinal perforation, and develop the imaging diagnosis and differential diagnosis of perforation peritonitis. Methods 36 cases of suspected perforation peritonitis were examined by CT scanning, among which 28 cases underwent surgery within 24 hours of CT scanning, and the region and the degree of peritonitis were confirmed by surgery and pathology. The other 8 cases were definitive diagnosed by clinical comprehensive indicators. The sensitivity, specificity and overall accuracy of diagnosis of 6 kinds of CT signs associated perforated peritonitis were calculated separately. Correlation coefficient method was used to test the preoperative CT diagnosis and pathologic. Results Correct diagnostic rate of using the main CT signs of perforation peritonitis before operation was 86.1% (31/36). The main CT manifestations of Perforation peritonitis were celiac free gases, peritoneal effusion, thickening of the gastrointestinal tract wall, wall peritoneal thickening, mesenteric adipose stripe and intestinal stasis dilatation. The sensitivity separately were 82.1%, 92.8%, 67.8%, 75%, 89%, 53.6%, and the specificity separately were 25%, 37.5%, 62.5%, 100%, 89.3%, 75%. Peritoneal effusion, wall peritoneal thickening and mesenteric adipose stripe have significant correlation with peritonitis diagnosis (P<0.05). Conclusion CT signs can make more accurate diagnosis to perforation peritonitis prior to surgery.