Objective To determine the dimensions of trachea and main bronchi by bronchoscopy, and provide theoretical basis for diagnosis and treatment of airway diseases. Methods Thirty consecutive adult patients with minor pulmonary diseases were enrolled for bronchoscopy examination. The lengths of the trachea and main bronchus were determined by bronchoscopy and the transverse diameter and anteroposterior diameter of the fifth and tenth tracheal rings above carina were determined. Results The lengths of the trachea and left and right main bronchus were (13.09±1.40) cm, (4.57±0.51) cm and (1.80±0.72) cm, respectively. Magnification times was 10.72 when apex of Olympus BF-260 was 1 cm from measuring object. Based on the magnification times determined in our study, the transverse diameter and anteroposterior diameter of the fifth tracheal ring were (2.76±0.32) cm and (2.44±0.27) cm. Similarly, the transverse diameter and anteroposterior diameter of the tenth tracheal ring were (2.97±0.33) cm and (2.72±0.36) cm. The transverse diameter and anteroposterior diameter of the tenth tracheal ring were significantly larger than those of the fifth tracheal ring (allP＜0.05). Conclusion Based on the magnification times determined in our study, dimension measurement of the trachea and main bronchi by bronchoscopy can objectively reflect anatomic structure of airway in physiological quiet breathing status.