Pulmonary hypertension is a common clinical syndrome, which seriously affects the quality of life and survival of patients. Pulmonary hypertension (PH) is defined as an increase in mean pulmonary arterial pressure (mPAP) to ≥20 mmHg at rest as measured invasively by right heart catheterisation (RHC). Pulmonary hypertension can be divided into five types, among which pulmonary hypertension caused by chronic pulmonary diseases and/or hypoxia is called Group 3 pulmonary hypertension, which is the most important factor of pulmonary heart disease. The drugs currently used to treat patients with PAH (prostanoids, endothelin receptor antagonists, phosphodiesterase-5 inhibitors, sGC stimulators) have not been sufficiently investigated in Group 3 PH, except indirect treatment methods such as improving hypoxia and controlling infection. Recombinant human brain natriuretic peptide (rhBNP) is a biological agent with a molecular weight of 3664Da synthesized by DNA technology. It is availble in China. It has many functions such as diuresis, vasodilation, inhibition of renin-angiotensin-aldosterone and sympathetic nervous systems, etc. RhBNP has been suggested in patients with acute myocardial infarction and congestive heart failure. In view of the dilating effect of rhBNP on pulmonary vessels, it is speculated that rhBNP may reduce type 3 pulmonary hypertension. Based on this hypothesis, we conducted a preliminary clinical trial. The results showed that, compared with the placebo group, after rhBNP was continuously pumped for 24 hours, the pulmonary artery hemodynamic indexes continuously monitored by Swan-Ganz catheter were significantly improved. In view of the pharmacological effect of rhBNP and our previous clinical trial results, this study intends to conduct a prospective, multicenter, placebo-controlled, double-blind clinical trial to evaluate the efficacy and safety of rhBNP in the treatment of patients with group 3 pulmonary hypertension.