Objective To investigate the clinical effects of early drainage of ascites for the treatment of se-vere acute pancreatitis (SAP) . Method A total of 30 patients with ASP were enrolled depending on the criteria of ASP with age over 18 years admitted to ICU from Jan 2007 to Jan 2009. Patients, who died within 24 hours after ad-mission, and had Marshall Score over 20, definite infection in abdominal cavity and previous laparotomy,were ex-cluded. Intravesical pressure/intra-abdominal pressure was measured in all patients with a Forley' s catheter insert-ed through urethra into bladder. All patients were randomized to have either routine treatment alone (group A, n = 16) or routine treatment with early drainage of ascites (group B, n= 14). The scores of APACHE II and Mar-shall of all patients were recorded at admission and on the 3 rd, 7 th and 10th days. Concurrently, the measure-ments of the intra-abdominal pressure (1AP), the amount of aseites drained from abdominal cavity, the bowel sound, the volume of gastrointestinal decompression, and the days of mechanical ventilation employed were docu-mented, and the levels of plasma pre-albumin (PA) and C-reactive protein (CRP) were measured as well. The analyses of variance and t-test were used for the comparison of inter-and between groups. P ＜ 0.05 was consid-ered statistical significance. Results There was no statistical difference in all measurements between two groups at admission. From the 3rd day on, there were significant distinctions between two groups in the score of APACHE Ⅱ [(16.81 ±3.19) vs. (25.36±12.58, P ＜0.05), the score of Marshall [(6.09±3.71) vs. (11.47±4.02), P ＜0.05], the IAP [(12.7±6.3) vs. (22.5±5.1), P ＜0.05], the level of CRP [(198.65 ±94.37) vs. (304.16 ±86.51), P ＜0.05], and the volume of gastrointestinal decompression [(654±290) mL vs. (1033±451) mL, P ＜0.05]. The time of mechanical ventilation employed in group B was obviously shorter than that in group A [(4.07±1.78) days vs. (7.13±2.22) days]. The survival rate within 28 days in group B was obviously higher (92.86% vs. 81.25%, P ＜0.05). Conclusions The pancreatitis-associated ascites plays an important role in the course of the SAP. Early drainage of ascites can obviously blunt the inflammatory re-action of the ASP, benefiting the functional recovery of intestine and respiratory system, improving the general con-dition of patients with ASP, and increasing the survival rate.