The present invention belongs to the field of medicine, and relates to use of cannabidiol (CBD) in the treatment of pulmonary arterial hypertension. The CBD can be used as the only active ingredient or combined with other active ingredients to prepare a medicament for treating pulmonary arterial hypertension. Specifically, the present invention relates to use of any one selected from (1) to (3) in the preparation of a medicament for treating and/or preventing pulmonary arterial hypertension: (1) CBD, (2) a plant extract containing the CBD; and preferably, the plant extract is a cannabis extract, and (3) a pharmaceutical composition containing the CBD and one or more pharmaceutically acceptable adjuvants. In the present invention, upon experimental researches, it has found that the CBD has the function of inhibiting pulmonary arterial hypertension, and is especially suitable for treating the pulmonary arterial hypertension caused by hypoxemia.