This is the first and largest randomized, controlled, blinded trial that evaluates the efficacy of autologous cord blood mononuclear cells infusion as a prevention therapy for BPD or death. The results of this trial will provide valuable clinical evidence for recommendations on the management of BPD in extremely preterm infants. In this prospective, randomized controlled double-blind multi-center clinical trial, 140 extremely preterm neonates less than 28 weeks are randomly assigned to receive intravenous autologous cord blood mononuclear cells infusion (targeted dose of 5×107cells/kg but no less than 1×107cells/kg) or placebo ( normal saline) within 24 hours after birth in a 1:1 ratio using a central randomization system. The primary outcome is survival without bronchopulmonary dysplasia at 36 weeks of postmenstrual age or discharge home. The secondary outcomes will include mortality rate, BPD severity, other common preterm complication rate, respiratory support duration, the length and cost of hospitalization and long term outcomes after two years follow up post infusion.