COPD and sleep apnea dyspnea syndrome represent two of the most common chronic lung diseases. It is reported that the prevalence of COPD with sleep apnea dyspnea syndrome is also very high. COPD and sleep apnea may have pathological or genetics interactions so that patients having both disorders tend to have worse outcomes than either condition alone. Data reflecting the prevalence, disease course and outcome of overlap syndrome is very limited in China. Therefore, the aim of the study is to describe the prevalence, treatment and outcome in Chinese patients and exploring the underlying interaction mechanism.