Objective To investigate the efficacy and safety of preemptive one lung ventilation(OLV)combined with disconnection technique for lung collapse during OLV with bronchial blocker(BB)in thoracoscopic surgery.Methods 75 patients who were scheduled for elective left lung segment or lobectomy under thoracoscopy were randomly divided into preemptive OLV group(group A),disconnection technique group(group B)and preemptive OLV combined with disconnection technique(group C),25 cases in each group.The time of complete lung collapse,surgeon satisfaction,pre-thoracic preparation time,OLV time,operation time,and occurrence of hypoxemia[percutaneous arterial oxygen saturation(SpO2)<90%]within 20 minutes after the onset of OLV were recorded;The lung collapse score(LCS)at the moment of pleural cavity opening(T0),1 min(T1),5 min(T2),10 min(T3)and 20 min(T4)after pleural cavity opening were recorded.Results Compared with group A and B,the complete lung collapse time in Group C was significantly shortened,and the surgeon satisfaction was significantly improved,the differences were statistically significant(P<0.05).There was no statistical significance in the complete lung collapse time and surgeon satisfaction between group A and B,the differences were not statistically significant(P>0.05).Compared with group A,the LCS at T0 in group B was lower than that in group A,but significantly higher at T1,the differences were statistically significant(P<0.05).The LCS at T1,T2,T3 and T4 in group C were significantly higher than those in group A and group B,the differences were statistically significant(P<0.05).The value of SpO2 at T2 in group C was obviously lower than that in group A and group B,the difference was statistically significant(P<0.05).Conclusion Preemptive OLV combined with disconnection technique can improve the lung collapse of the non-ventilated lung during OLV with BB in thoracoscopic surgery,shorten complete lung collapse time,with higher surgeon satisfaction,and higher LCS score during OLV.However,SpO2 during OLV still needs to be monitored.