Objective To compare the effects of Coopdech endobronchial blocker placed outside the endotracheal tube and single lumen endotracheal tube on the one-lung ventilation in infants and young children undergoing thoracoscopic surgery.　Methods　A total of 40 children with congenital pulmonary cystic lesions who underwent elective partial pulmonary resection were randomly divided into a Coopdech bronchoblocker group (group C) and a single-lumen endotracheal tube group (group E) (n=20). Under a fiberoptic bronchoscope, Coopdech endobronchial blocker was placed outside the endotracheal tube into the affected side in group C, and single-lumen tube was placed into the unaffected side in group E. The degree of lung collapse was observed, the rate of excellent cases of lung collapse and lung collapse time were recorded. The changes in mean arterial pressure (MAP), heart rate, arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2) and airway pressure (Paw) were recorded 5 min after dual-lung ventilation (T1), 20 min after one lung ventilation (T2), 40 min after one lung ventilation (T3), and 60 min after one lung ventilation (T4) were recorded. The success rate of first intubation, intubation time, one lung ventilation time, operation time, recovery time were recorded.　Results　There was no significant difference in the excellent rate of lung collapse between the two groups (P>0.05). The lung collapse time in group C was significantly longer than that in group E (P<0.05). There were no significant differences in MAP, heart rate between the two groups (P>0.05). At T2, T3 and T4, PaO2 in group C was significantly higher than that in group E (P<0.05), and PaCO2 and Paw were significantly lower than those in group E (P<0.05). The success rate of first intubation in group C was significantly higher than that in group E (P<0.05), the intubation time and the operation time were shorter than that in group E (P<0.05). There were no significant differences in the one lung ventilation time and recovery time between the two groups (P>0.05).　Conclusions　Compared with single lumen endotracheal tube, the Coopdech endobronchial blocker which is placed outside the endotracheal tube through fiberoptic bronchoscopy can provide better one-lung ventilation effect in infant and young children with congenital pulmonary cystic lesions undergoing thoracoscopic surgery.