Objective Previous investigations suggest that severe acute pancreatitis (SAP) is one of the main causes of intra-ahdominal pressure (lAP) increase. The aims of this study were, to evaluate the increased IAP in patients with SAP and the correlation between LAP and severity or prognosis. Method Data of 75 SAP patients admitted to Xuan-Wu Hospital of Capital Medical University intensive care unit with SAP from January 2000 to Jan-uary 2008 were collected. All the patients had at least one organ dysfunction, and they were diagnozed with en-hanced CT, lAP were monitored in the 56 patients. The 56 patients were divided into three groups according to IAP, group A (7- 15 mmHg), group B (16-25 mmHg) and group C (26-31 mmHg). Maximal APECHE Ⅱscore, maximal Ranson score, maximal C-response protein (CRP), maximal arterial lactate, maximal creatinine, organ dysfunction, length of stay and mortality were compared. Results The 56 patients (24 male and 32 female)with average age of (52±14.1) years (ranging 21 - 72 years) and average body mass index (BMI) of 28±12.5(ranging 21 - 35) were monitored with IAP. The etiologic causes of SAP were biliary in 27 patients, alcohol in 14cases, hyperlipidemia in 11 cases and idiopathic in 4 cases. The rate of intra-abdominal hypertension was 89% (50/56), and 32% (18/56) patients complicated with abdominal compartment syndrome. There were 22, 26 and 8 patients in the A, B and C groups respectively. With the increasing of IAP, the maximal APACHE Ⅱ, maximal Ranson score, maximal CRP, maximal creatinine, organ dysfunction and mortality were also increased significant-ly. The mortality of the three groups was 13.6% (3/22), 23.1% (6/26) and 62.5% (5/8) respectively (χ2 =7.56, p = 0.023), and the total mortality of the 56 patients was 25%. The hospital stay of the three groups had no significant differenee(F = 2.23,P = 0.117). Conclusions IAP may be one of the markers used to evaluate the severity of SAP, and the monitoring of IAP is useful to assess the prognosis in patients with SAP.