Objective To investigate the value of pleural effusion and C-reactive protein in severity evalua-tion and prognosis of acute pancreatitis. Methods Clinical data of 108 patients with acute pancreatitis were ana-lyzed retrospectively. AP classification was conducted on the basis of intensified CT examination and the clinical in-dexes including blood calculus, blood lipid, blood glucose and blood gas were measured. The criteria for diagnosis and severity evaluation of acute pancreatitis were based on results of chest X-ray, CT examination and CRP. The correla-tion between pleural effusion, CRP and the severity, etiology, prognosis of acute pancreaitis were analyzed. Results Of the 108 patients, mild acute pancreatitis (MAP) was found in 57 patients, and severe acute pancreatitis (SAP) in 51. Among SAP, 32 patients (62.75% ) developed pleural effusion, 38 patients (74.51% ) whose CRP > 20.00 mg/L,and 27 patients (52. 94%) had both pleural effusion and CRP > 20. 00 mg/L. There were 13 (22.81% ), 14 (24.56%) and 8 (14.04%) respectively among MAP. The difference between the two groups was sig-nificant(P<0.01). Among acute biliarv pancreatitis,9 patients (33.33%) developed pleural effusion and 15 (55.65%) whose CRP>20 mg/L and 9 (33.33%) had beth pleural effusion and CRP>20.00 mg/L; Among acholic AP,25 (65.79%) developed pleural effusion and 20 (52.63% ) whose CRP > 20.00 mg/L and 23 (60.53%) had beth pleural effusion and CRP>20.00 mg/L. Case fatality was also significantly different between group with pleural effusion,CRP >20.00 mg/L,both pleural effusion and CRP>20.00 mg/L,and group with non-pleural effusion,CRP≤20.00mg/L,non-pleural effusion or CRP≤20.00mg/L respectively(P<0.01). Conclusion Either pleural effusion or CRP can be used as independent prognostic parameters for severe acute pancreatitis,and the combined use of these two parameters is the most reliable.