Pulmonary arterial hypertension (PAH) is a progressive disease with limited effective therapies that can be lethal in the terminal stage. Since the universal use of traditional PAH-specific drugs affecting the nitric oxide pathway, endothelin pathway and prostacyclin pathway, major advances to treat this devastating condition have been made. For example, it has been recently demonstrated that PAH is associated with various dysfunctional genes and molecular signaling pathways, abnormal metabolism and endocrine systems, inflammation and immune dysfunction. Numerous descriptions of novel mechanisms in PAH have been presented, and some new drugs targeted to ease, reverse or cure PAH have been developed at the laboratory-level and/or tested in clinical trials. There are also some investigated drugs that have shown promising efficacy and safety in animal models but have failed in human beings. Inspiringly, immunotherapies also seem to be valuable therapies for PAH patients. In this review, we update the advances in investigational pharmacotherapy and immunotherapy of PAH. Hopefully this work can help promote more non-invasive treatment for PAH patients.