Objective To evaluate the value of the Bedside Index for Severity in Acute Pancreatitis (BISAP) in diagnosing severe acute pancreatitis. Methods Sixty-eight patients with suspected diagnosis of severe acute pancreatitis were collected and were scored by BISAP, APACHE Ⅱ , Ranson and CTSI scoring systems, respectively. BISAP scoring system included the blood urea nitrogen, impaired mental status,systemic inflammatory response syndrome, age, and pleural effusion. The diagnosis criteria of severe acute pancreatitis was BISAP ≥ 3 points or APACHE IⅡ ≥ 8 points, Ranson ≥ 3 points, CTSI ≥ 3 points. The diagnostic accuracy of SAP of these scoring systems was calculated. Results Among these 68 cases, 63.2％(43/68) were graded ≥ 3 points in BISAP scoring system;60.3％ (41/68) were marked ≥8 points in APACHE Ⅱ scoring system; 60.3％ (41/68) were scored ≥ 3 points in Ranson scoring system; and 67.6％(46/68) were scored ≥3 points in CTSI scoring system. There was no statistical difference between BISAP scoring system and other three scoring systems in diagnosing severe acute pancreatitis. Conclusions As a new and simple scoring system, BISAP scoring system can be widely used in the diagnosis of severe acute pancreatitis.