Objective：To compare the advantages and disadvantages of pulmonary ultrasound and fiberoptic bronchoscopy in the localization of endobronchial blocker. Methods：90 patients undergoing elective left thoracotomy for esophageal cancer were randomly divided into two groups：with 45 in each. After anesthesia induction，7.5 cm reinforced tracheal tube was inserted orally，and then the endobronchial blocker was placed blindly to the unilateral bronchus. The position of blocker was located and the effect of pulmonary isolation was judged respectively by pulmonary ultrasonography(group L)and fiberoptic bronchoscopy(group B). Patients were placed in right lateral position and then the blocker position was judged again. The total time needed to judge the pulmonary isolation in group L and group B，the times of intraoperative blocker adjustment，the satisfaction score of intraoperative pulmonary collapse，and the levels of MAP，HR and peak airway pressure(PAW)before and during the two positioning were recorded. Results：There was no significant difference in lung isolation time，lung collapse satisfaction score and intraoperative cuff adjustment times between group L and group B(P ＞ 0.05). Compared with those before positioning，HR，MAP and PAW in group L during the blocker localization had no significant changes(P ＞ 0.05). The levels of HR，MAP and PAW in group B during twice blocker positioning were significantly higher than those before fiberoptic bronchoscope implantation(P ＜ 0.05). Conclusion：The pulmonary isolation effect of endobronchial blocker judged by pulmonary ultrasound is similar to that of fiberoptic bronchoscope，but the effect of pulmonary ultrasound on hemodynamics is less than that of fiberoptic bronchoscopy.