OBJECTIVE To explore the characteristics of lung function in preterm infants with varying degrees of bronchopulmonary dysplasia(BPD). METHODS There were 407 infants (278 males and 129 females) were recruited from Shenzhen Children' Hospital between January 2011 and October 2012.Among them 188 term infants (term group)and 113 preterm infants (non-BPD preterm group) were selected as controls. A total of 106 BPD infants from the observation group were divided into mild(n = 48), moderate (n = 42) and severe(n = 16) sub-groups according to the definition of BPD. Infants with diseases interfering with lung function, such as congenital heart disease, congenital diaphragmatic hernia, or thoracic wall deformities, were excluded. Lung function was tested at a postmenstrual age (PMA) of 44 weeks.q test, Dunnett C test and Spearman analysis were used for statistical analysis. RESULTS The age range was 17-116 d, test weight range 1.83-7.00 kg and test height range 40.0-64.0 cm.In non-BPD preterm group, the respiratory rate (RR) was higher than that in term group ((50 ± 13) vs (44 ± 10) times/min,P < 0.01) ,while the tidal volume(TV), ratio of time to peak tidal expiratory time and expiratory time (Tpef/Te) and peak expiratory flow(TPEF) were all less than those in term group ((25 ± 9) vs (29 ± 7)ml,29% ± 9% vs 33% ± 8%, (59 ± 23) vs (65 ± 25)ml/s,all P < 0.05) .Neither functional residual capacity(FRC) nor lung clearance index (LCI) had significant statistical difference between two groups ((20 ± 5) vs (19 ± 5)ml/kg, 8.4 ± 2.8 vs 8.7 ± 3.4, all P > 0.05)) . In moderate and severe BPD groups, RR ((57 ± 9), (58 ± 10) times/min) were both higher than that in non-BPD group(both P < 0.05) while RR in mild group ((53 ± 13)times/min)had no statistical significant difference with non-BPD group (P > 0.05). The values of TV and LCI in mild, moderate and severe BPD groups have no statistical significance with non-BPD group (all P > 0.05). Except for mild BPD group(24% ± 13%, (18 ± 5)ml/kg), Tpef/Te and FRC in both moderate and severe groups (20% ± 9% and 18% ± 5%, (15 ± 3)and (15 ± 4)ml/kg)were less than those in non-BPD group(all P < 0.05). Only in severe BPD group ((85 ± 11)ml/s), TPEF was higher than that in non-BPD group(P < 0.05). Correlation analysis showed that, except for LCI, all of these parameters were significantly associated with the degree of BPD(all P < 0.05). CONCLUSIONS For BPD and non-BPD preterm infants, there are various changes in respiratory rhythm, lung volume, ventilation inhomogeneity, ventilatory efficiency and small airway resistance. The increases of pulmonary elastic recoil and degree of major airway constriction are obvious in moderate and severe BPD infants.