Objective To study the role of interleukin-33 (IL-33) in the development and progression of bronchopulmonary dysplasia (BPD) in preterm infants. Methods A prospective cohort study was performed on 128 preterm infants with a gestational age of ≤ 32 weeks and/or a birth weight of ≤ 1 500 g. They were classified to a non-BPD group with 50 infants, a mild BPD group with 32 infants, a moderate BPD group with 30 infants, and a severe BPD group with 16 infants. Related data were collected, including antepartum factors of mothers (antepartum hormone and chorioamnionitis), intrapartum factors of preterm infants (sex, gestational age, birth weight, mode of birth, and birth asphyxia), treatment after birth (pulmonary surfactant, duration of invasive ventilation, duration of noninvasive ventilation, duration of parenteral nutrition, and length of hospital stay). The high-risk factors for BPD were analyzed. ELISA was used to measure the serum level of IL-33 in preterm infants on days 1, 14, and 28 after birth. The serum level of IL-33 was compared between groups at different time points after birth. The preterm infants with moderate or severe BPD were treated with conventional corticosteroid therapy (DART regimen), and the serum level of IL-33 was measured before and after treatment. Results There were significant differences between the preterm infants with BPD and those without BPD in the incidence of maternal chorioamnionitis, gestational age, birth weight, the incidence of birth asphyxia, duration of invasive ventilation, duration of noninvasive ventilation, duration of parenteral nutrition, and total length of hospital stay (P < 0.05). There were significant differences in the above indices among the preterm infants with different severities of BPD (P < 0.05). On days 1, 14, and 28 after birth, the infants with BPD had a significantly higher serum level of IL-33 than those without BPD, and the serum level of IL-33 tended to increase with the severity of BPD and over the time after birth (P < 0.05). The preterm infants with moderate or severe BPD had a significant reduction in the serum level of IL-33 after the treatment with DART regimen (P < 0.05). Conclusions Serum IL-33 is closely associated with the development and severity of BPD. Anti-inflammatory therapy with DART regimen can decrease the serum level of IL-33.