Inclusion Criteria:  Eligibility requirements for neonates:  The gestational age is less than 32 weeks The preterm neonates are diagnosed with BPD and need invasive ventilation Extubation and subsequent noninvasive ventilation is ready to be carried out  Exclusion Criteria:  one of the following conditions is needed:  there were no intraventricular hemorrhage(IVH) grades 3 or 4 major congenital anomalies parents' decision not to participate