Objective：To study the clinical value of the collapse angle of flow - volume（F - V）curve in assessment of clinical phenotype and severity of chronic obstructive pulmonary disease（COPD）patients. Methods：A total of 101 subjects who underwent pulmonary function tests from December 2021 to December 2022 at the First Affiliated Hospital of Nanjing Medical University were selected for this study. Subjects in the angle group were 33 stable COPD patients with collapse angle of F -V curve. The non -angle group including 38 cases of stable COPD patients without collapse angle，who matched with the angle group in forced expiratory volume in the first second as a percentage of predicted value（FEV₁%pred）. The control group including 30 subjects without previous cardiopulmonary disease and had normal lung function. Basic information，clinical symptom scores（CAT score，mMRC score），pulmonary function parameters and daily exercise finger pulse oxygen parameters were collected and compared among the groups. Multifactorial logistic regression was used to analyze the factors associated with the collapse angle of F-V curve. The predictive value of the collapse angle of F - V curve for acute exacerbation of COPD within one year of follow - up was analyzed by receiver operating characteristic（ROC）curve. Results：Pulmonary function was severely impaired in the angle group，with FEV₁ and forced vital capacity （FVC）of 0.91±0.24 and 2.11±0.63，respectively. CAT score，mMRC score，and ΔSpO₂ of the angle group were higher than those of the non-angle group and the control group. SpO_2L of the angle group after walking exercise was lower than that of the non-angle group and the control group（P ＜ 0.05）. CAT score ≥12，mMRC score ≥2，and ΔSpO₂≥13% were main related factors of the emergence of the collapse angle of F-V curve. The area under the ROC curve of the collapse angle of F-V curve for predicting the acute exacerbation of COPD was 0.777. The sensitivity and specificity of prediction were the best when the angle was ＜129.1°，which were 72.73% and 67.35%，respectively. Conclusion：When the collapse angle of F-V curve appears in patients with COPD，their lung function is often severely impaired. They are more prone to post-activity hypoxemia and acute exacerbations. Therefore，attention should be paid to the presence of the collapse angle of F -V curve in the pulmonary function report of COPD，in order to recognize the high - risk group of COPD as early as possible.