Objective To investigate the impact of relevant factors in mechanical ventilation on intra- abdominal pressure in patients with ALI/ARDS by continuous monitoring of intra-abdominal pressure. Methods A total of 116 ALI/ARDS patients treated with mechanical ventilation in ICU were enrolled in this study. Intra-abdominal pressure (IAP) was recorded continuously. Meanwhile ventilator parameters, arterial blood gas analysis, hemodynamic variables, and as well as the levels of IL-4, IL-8 and TNF-α in blood and bronchial alveolar lavage fluid (BALF) were determined and recorded. The detection of risk factors for intra-abdomen hypertension (IAH) were carried out using multivariate stepwise logistic regression. ROC curve analysis used to estimate the diagnostic performance of these parameters for IAH. Results The oxygenation index (PaO2/FiO2) in patients with IAH after 2 hours' mechanical ventilation was significantly lower than that in patients with normal intra-abdomen pressure (IAP) (P <0.01) ; PEEP and RR in mechanical ventilation were higher in IAH group (P <0.01 or P=0.001) ; Mean artery pressure (MAP) , ejection time percent (ET) , stroke volume (SV) , cardiac index (CI) were lower in IAH group than those in normal IAP group (P <0.01) ; the levels of IL-4, IL-8 and TNF-α in blood and bronchial alveolar lavage fluid were higher in IAH group than those in normal IAP group (P <0.01) ; IAH patients have a higher mortality on 28 d (Log rank test, P=0.023). Poor oxygenation index (PaO2/FiO2) after 2 hours' ventilation, high PEEP setting, low MAP, ET, SV, CI and elevated IL-4 in the BALF were resulted in increasing risk of IAH for ARDS patients under mechanical ventilation support. Conclusions The monitoring of intra-abdominal pressure should be emphasized for ALI/ARDS patients when mechanical ventilation was employed. PaO2/FiO2, SV and IL-4 in BALF might be the independent risk factors of IAH. Key words: Mechanical ventilation; Acute lung injury/acute respiratory distress syndrome; Intra- abdominal pressure (IAP); Intra-abdominal hypertension (IAH); Logistic regression