[ ] Objective In order to investigate the correlation between thickening swollen lesser omental sac by ultrasound and APACHEⅡscoring in acute pancreatitis. Methods The thickening swollen lesser omental sac were detected by ultrasound in 29 cases with acute pancreatitis from January 2016 to June 2017.The results were compared with the acute physiology and chronic health evaluation(APACHEⅡ)scores. The degree of APACHE II score of the patients with acute pancreatitis and the thickening swollen lesser omental sac were compared between the patients in ICU and the patients not in ICU. Results It was obvious to correlate thickening swollen lesser omental sac to APACHE II Scores(Y=0.1125+0.4359X,r=0.78,P<0.05). The degree of APACHE II score of the patients with acute pancreatitis and the thickening swollen lesser omental sac of the patients in ICU were significantly different from that of the patients who did not stay in the ICU. ( P<0.05). Conclusions Based on these results．It would seem logical to use thickening swollen lesser omental sac to assess the severity of acute pancreatitis．