Objective: To study the clinical value of the collapse angle of the flow-volume curve (F-V curve) in the assessment of the clinical phenotype and severity of COPD patients. Methods: Subjects who underwent pulmonary function tests from December 2021 to December 2022 at the First Affiliated Hospital of Nanjing Medical University were selected for the study. The subjects in the Angle Group were 33 stable COPD patients with the collapse angle of the flow-volume curve. 38 cases of stable COPD patients without collapse angle, who matched with FEV1 in the pinch group, were the Non-Angle Group.30 subjects without previous cardiopulmonary disease were the control group. Basic data, clinical symptom scores (CAT score, mMRC score), pulmonary function parameters and daily exercise finger pulse oxygen parameters were collected and compared between the groups. Multifactorial logistic regression was used to analyse the factors associated with the collapse angle of the flow volume curve. The predictive value of the collapse angle of the flow volume curve for acute exacerbation of COPD within 1 year of follow-up was analyzed by ROC curve. Results: Pulmonary function was severely impaired in the Angle Group, with FEV1 and FVC of 0.91(SD 0.24) and 2.11(SD 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 (P<0.05); SpO2L during walking exercise from the Angle Group 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 the main correlates of the emergence of the collapse angle of the flow volume curve in the Angle Group. The AUC of the angle of the collapse angle of the flow volume 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 the F-V curve appears in patients with COPD, their lung function is often severely impaired. Those patients with CAT scores ≥12 and mMRC scores ≥2 were multisymptomatic patients and belonged to group E of the GOLD subgroup. They were more prone to post-activity hypoxemia and acute exacerbations. Therefore, attention should be paid to the presence of the collapse angle of the F-V curve in the pulmonary function report of COPD, in order to recognize the high-risk group of COPD as early as possible. Medical interventions and management programs should be provided to improve the symptoms and quality of life of these COPD patients and to prevent acute exacerbations.