Objective To discuss oral nursing frequency of patients undergoing orally mechanical ventilation in order to ensure the oral cleanness of patients with the least oral nursing frequency and prevent the occurrence of ventilator associated pneumonia (VAP). Methods 36 patients undergoing orally me-chanical ventilation were randomly divided into groupA, B, C and D with 9 cases in each group, which all adopted 0.5% of pevidone iodine solution for oral nursing, time intervals of oral nursing were 4 hours, 6 hours, 8 hours and 12 hours. After the oral care and oral care before the next oropharyngeal samples for se-mi-quantitative bacterial colony counts, bacterial strain identification were obtained. The incidence rate of VAP was also compared and the results underwent χ2 test. Results Significant difference was seen in bacterial colony counts, especially during the time interval of 6 hours and 12 hours. No significant differ-ence was seen in incidence of VAP between the 4 groups. Conclusions The desirable frequency of oral nursing was every 6 hours on the premise of prevention of VAP.