Sarcopenia is influenced by multiple factors, including psychological aspects. This study aimed to explore the relationships among depressive symptoms, dyspnea-related fear, and sarcopenia, with a focus on the mediating role of physical activity. A cross-sectional study was conducted among 348 COPD patients at a tertiary hospital in Western China from July 2023 to July 2024. Sarcopenia was assessed according to the 2019 AWGS criteria, including hand bioelectrical impedance analysis (BIA), and grip strength testing. Depressive symptoms, dyspnea-related fear, and physical activity were evaluated through self-reported measures using the depression subscale of the Hospital Anxiety and Depression Scale (HADS), the Breathlessness Beliefs Questionnaire (BBQ), and the International Physical Activity Questionnaire Short Form (IPAQ-SF), respectively. Logistic regressions analyses explored associations among depressive symptoms, dyspnea-related fear, and sarcopenia. Maximum Likelihood (ML) estimation was employed using Mplus software to evaluate the mediating effect of physical activity on the relationships. The prevalence of sarcopenia among COPD patients was 60.3%. In the logistic regression analysis with sarcopenia as the dependent variable, physical activity levels (OR = 0.508, = 0.019) and depressive symptoms (OR = 1.079, = 0.029) were statistically significant, while BBQ scores were not (OR = 1.031, = 0.070). Mediating analyses revealed that depressive symptoms directly increased the risk of sarcopenia (β = 0.076, = 0.042) but did not do so indirectly via physical activity (β = 0.056, = 0.146). Conversely, dyspnea-related fear had an indirect effect on sarcopenia through physical activity, with a borderline statistical significance (β = 0.053, = 0.049). This study highlights the critical role of psychological factors in sarcopenia development among COPD patients, with physical activity serving as a significant mediator. These findings underscore the need for integrated rehabilitation strategies addressing both psychological and physical activity barriers to improve outcomes for COPD patients.