Objective To estimate the degree of the angle between left principal bronchus and trachea, and it is correlative with the pulmonary function in the patients with rheumatic mitral valve disease. Methods According to various degree of angles between left principal bronchus and trachea,53 patients were divided into three groups, group 1: angle between left principal bronchus and trachea less than 50 degree, group 2: between 50 and 64 degree, group 3: between 65 and 79 degree. The pulmonary function tests,ultrasonic cardiography and left principal bronchus X-ray tomographic film were carried out in three groups before operation. Compare pulmonary function data with different angle between left principal bronchus and trachea in three groups. Results Exception of vital capacity ,residual volume and total lung capacity,the rest markers of lung function showed significant differences (Plt;0.05) in three groups. The correlation of the angle between left principal bronchus and trachea and the ratio of residual volume and total lung capacity among three groups were positively correlative, and the other parameters of lung function were negatively correlative (Plt;0.01). Conclusion The degree of the angle between left principal bronchus and trachea is positively correlative with the extent of pulmonary function impairing.