Objective To observe effect of using ambroxol to humidify of airway during mechanical ventilation to treat severe pneumonia in infants,and to explore dynamic changes of respiratory mechanics.Methods Sixty-five infants with severe pneumonia need ventilator treatment according the diagnosis criterion were divided into 2 groups by random digits table method:experimental group (33 cases) and control group (32 cases).Experimental group was used ambroxol and control group was used 0.9％ sodium chloride,each 2 ml intratracheal instillation,and then took the balloon pressurized oxygen 30 s,followed by ventilator,after 24 h.Changes of respiratory mechanics indexes were observed before and after treatment,including:mean airway resistance,lung dynamic compliance,work of breathing,airway plateau pressure.Respiratory mechanics values were recorded before and after treatment.Results After treatment for 24 h,the index in experimental group were better than those in control group.Mean airway resistance were (0.68 ± 0.04) cmH2O/ (L·s) and (0.57 ± 0.05) cmH2O/ (L·s),1 cmH2O =0.098 kPa,lung dynamic compliance were (3.17 ± 0.81) ml/kPa and (2.56 ± 0.69) ml/kPa,work of breathing were (0.54 ± 0.08) J/L and(0.41 ± 0.06) J/L,airway plateau pressure were (2.23 ± 0.58) cmH2O and (2.12 ± 0.63) cmH2O.There were significant differences (P ＜ 0.05).The mechanical ventilation time in experimental group was significantly shorter than that in control group [(64.08 ± 13.92) h vs.(79.57 ± 19.64) h] (P ＜0.05).Conclusion Airway humidification using ambroxol can better treat severe pneumonia,reduce airway resistance and improve alveolar ventilation,shorten time on the machine.