Present treatment for chronic obstructive pulmonary disease (COPD) has a certain role in reducing COPD exacerbation and hospitalization, improving the life quality, and postponing the lung function decline. But for some patients with severe COPD, current treatment only partially alleviates the symptoms and has little role in the lung function decline. In this randomized, multicenter study, the investigators evaluate the safety and efficacy of bosentan in the treatment of grade Ⅲ or Ⅳ COPD patients with pulmonary hypertension detected by echocardiography. The primary endpoint is the frequency of COPD exacerbation, and the secondary endpoint includes changes of lung function, 6-min-walk distance (6-MWD), SGRQ score and mMRC/CAT score.

Inclusion Criteria:

• Aged 18 to 75
• Gold Ⅲ or Ⅳ stable COPD
• Pulmonary hypertension detected by echocardiography

Exclusion Criteria:

• Acute exacerbation of chronic obstructive pulmonary disease
• Untreated obstructive sleep apnea
• Restrictive (total lung capacity<60% predicted) lung disease
• Portal hypertension
• Chronic liver disease
• Transaminase increased to normal line more than 3 times; total bilirubin increased 2 times more than the upper limit of the normal value
• Left-sided or unrepaired congenital heart disease
• Patients with other serious heart diseases
• Patients with 1, 2, 4 and 5 categories of pulmonary hypertension
• Unable to complete the 6 minutes walk test
• Patients receiving other endothelin receptor antagonists
• No cooperation to complete