Abstract: Objective: To investigate the clinical characters of the early onset and late onset ventilator-associated pneumonia（VAP）in old patients.Methods: To retrospectively investigate old people who had VAP in PLA General Hospital.To compare the demographic and associated variables reflecting ventilation, blood examination,and drug exposure between the two group patients.Results: 30 episodes were early onset VAP and 46 episodes were late onset VAP.The patients with late onset VAP showed a lower PH, Albumin and higher PaCO₂.The duration of mechanical ventilation in patients with late onset was longer than patients with late onset. There are no difference in the components of microorganisms between early onset and late onset pneumonia. （Conclusion: The） choice of initial antibiotic therapy should not be based on the time of VAP.