OBJECTIVE To study the effects of intra-abdominal pressure (IAP) on respiratory system, circulatory system and renal function in rats. To investigate the difference between the direct measure and indirect measure methods (via inferior vena cava and bladder) for IAP. METHODS Sixty Sprague-Drawly (SD) rats were randomly divided into 5 groups with different IAP (IAP value of 1-5 groups was 5, 10, 15, 20, 25 mm Hg,respectively) and healthy control group, 10 rats in each group. The parameters of respiratory system, circulatory system, renal function, and IAP value were recorded. The correlation between direct and indirect measurement methods was also analyzed. RESULTS There were no significant differences in above parameters between IAPI and healthy control groups. Compared with those in healthy control group, PaO2 significantly decreased (P < 0.05), SCr and BUN increased significantly in IAP2 group (P < 0.05). Other indexes in IAP3, IAP4 groups increased (P < 0.05 or P < 0.01) except for respiratory frequency(RF) and MAP (P > 0.05). PaO2 and MAP decreased (P < 0.01), and other indexes increased (P < 0.05 or P < 0.01) in IAP5 group. The values obtained from the indirect measure method were positively correlated with that from the direct measure method (r = 0.937, 0.955, P < 0.01, respectively). CONCLUSIONS IAP can affect respiratory system, circulatory system and renal function in different degrees in rats. The indirect measure method can replace the direct measure method for IAP measure with little injuries.