Appropriate use of antibiotics in the PCR group was 73.6% higher than that in the control group p<0.001; The duration of mechanical ventilation, the length of stay in the ICU and the length of hospital stay in the PCR group were significantly shortened with p<0.05; overall mortality was reduced in the PCR group with p= 0.022; but no change in the mortality rate due pneumonia at 7, 14, 28 days; It was necessary to apply multiplex real-time PCR to at least 6 patients to reduce one patient's death due to HAP, VAP.