Objective To investigate the relationship between the gastrointestinal function and ventilator-associated pneumonia (VAP) in critically ill patients who underwent invasive mechanical ventilation. Methods One-hundred and fifty-three cases of critically ill patients receiving mechanically ventilation were recruited in the study. After 5 days of ventilation, the gastrointestinal function score and the C-reactive protein (CRP) of each patient were recorded. The incidence of VAP was recorded during hospitalization. According to the incidence of VAP, all patients were divided intoaVAP group and a non-VAP group. The relationship between gastrointestinal function score and the incidence of VAP was analyzed. The relationship between CRP level and severity degree of VAP was also analyzed. Results VAP occurred in 42 cases with the incidence of 27.45%. The gastrointestinal function score (1.9±1.0 vs. 0.8±1.0, P < 0.05) and CRP level [(52.38±12.06) mg/L vs. (36.69±11.08)mg/L, P < 0.05] were both higher in the VAP group than those in the non-VAP group. At gastrointestinal function score of 0 - 3, the CRP levels were all higher in the VAP group than those in the non-VAP group (P < 0.05). The incidence of VAP was 8.33%, 23.68%, 45.45%, and 59.09% at gastrointestinal function score of 0, 1, 2 and 3, respectively, with significant differences between each other(P < 0.05). Conclusion For critically ill patients receiving invasive mechanical ventilation, the more severe the damage of gastrointestinal function is, the higher the incidence of VAP is, and the more serious the disease is.