Objective：To investigate bacterial colonization regularity in lower respiratory tract and ventilator tubing in patients with mechanical ventilation（MV） and etiology of ventilator-associated pneumonia（VAP） in the pediatric intensive care unit（PICU） and to provide empirical basis for the prevention of VAP and ventilator tubing management. Methods：Incidences of VAP in ventilated pa－tients in PICU or 4 th d and 7 th d were monitored targeted. Bacterial colonization of the lower respiratory tract and ventilator tubing and their relationship with MV replacement time were analyzed. Results：There were significantly differences in VAP incidences（P<0.05），positive bacterial culture rate and number of colonies in condensate and Y interface（P<0.05） as well as in consistency of posi－tive bacterial culture of lower respiratory tract and ventilator tubing（P<0.05） between the 4 th d group and the 7 th day group. Sewer enterobacter，acinetobacter baumannii and white candida mycoderma bacteria（39.2%） were key infection flora leading to VAP while acinetobacter baumannii，klebsiella pneumoniae burt’s bacteria and sewer enterobacter（47.3%） were primary infection flora coloniza－tion in the ventilator tubing. Conclusions：Etiology of VAP is closely related with bacterial colonization in ventilator tubing. Tubing replacement time of MV and bacteria colonization regularity affect incidence of VAP. Off-ventilation as soon as possible，attention to the bacterial contamination at the Y-type interface，standardized management of condensate and effective control of the ventilator tubing bacterial colonization are important to the clinical treatment of VAP and ventilator tubing management.