Objective To investigate the correlation between pectoralis muscle CT attenuation value (PMT) and cross-sectional area (PMA) with clinical characteristics, exercise tolerance, and respiratory failure in patients with chronic obstructive pulmonary disease (COPD), providing a new perspective for COPD assessment. Methods A total of 120 COPD patients (67 in stable phase, 53 in acute exacerbation phase) admitted between January 2020 and December 2023 and 60 healthy controls in the same period were included. All participants underwent chest CT scans for the measurement of PMA and PMT. Pulmonary function indices, 6-minute walk distance (6MWD), and quality of life scores were also collected from COPD patients. Statistical analysis was conducted to explore the relationship between PMA and PMT with clinical characteristics of COPD patients, and their predictive value for exercise tolerance in stable COPD patients and respiratory failure in acute exacerbation COPD patients was evaluated. Results Both PMA and PMT were significantly lower in the COPD patients compared with the control group (P<0.05) and were significantly correlated with pulmonary function, exercise capacity, and quality of life (P<0.05). PMA was identified as an independent risk factor for exercise intolerance in stable COPD patients (OR=1.261, 95%CI 1.075-1.496, P=0.004). Receiver operating characteristic (ROC) curve analysis revealed an area under curve (AUC) of 0.849 with a cut-off value of 23.72 cm² for PMA. Both PMA (OR=1.141, 95%CI 1.002-1.299, P=0.046) and PMT (OR=1.178, 95%CI 1.085-1.293, P<0.001) were independent risk factors for respiratory failure in acute exacerbation COPD patients. The ROC curve analysis showed an AUC of 0.804 with a cut-off value of 24.15 cm² for PMA and an AUC of 0.831 with a cut-off value of 37.65 Hu for PMT. Conclusions Pectoralis muscle PMA and PMT can serve as effective indicators for assessing the severity and prognosis of COPD. A lower pectoralis muscle PMA is a risk factor for exercise intolerance in patients with stable COPD, while lower pectoralis muscle PMA and PMT are risk factors for the development of respiratory failure in patients with acute exacerbations of COPD.