unassigned: To investigate the effect of exogenous Apelin on pulmonary artery hypertension (PAH) and its related mechanism. unassigned: 26 male SD rats were randomly divided into Control group ( =6), Model group ( =10) and Intervention group ( =10). The rat model of PAH was established by left pneumonectomy combined with monocrotaline injection (PE+MCT) in the Model group and the Intervention group, while the Control group rats were opened chest cavity and injected the same amount of normal saline. From the 2nd week after operation, the Intervention group was intraperitoneally injected with 10 nmol/(kg·d) Apelin-13 for 3 weeks, while the Control group and Model group were injected the same volume of normal saline. The mean pulmonary arterial pressure (mPAP) was measured and the right ventricular hypertrophy index ( ) was calculated in all three groups of rats at the 5th week after operation. The pulmonary tissue HE staining was performed to observe the pulmonary tissue and pulmonary vascular morphology. Protein LC3 was detected by immunofluorescence staining of lung tissues, the mRNA expression level of 62 and Beclin-1 in lung tissues was measured by RT-PCR, and the protein expressions of LC3, LC3-Ⅱ/LC3-Ⅰ, P62 and Beclin-1 in lung tissues were measured by Western blot. unassigned: Compared with the Control group, the Model group showed increased mPAP and ( <0.05), disordered pulmonary tissue structure and thicker pulmonary vascular wall. In Model group rats, expression of LC3 protein and LC3-Ⅱ/LC3-Ⅰ increased in lung tissues, and the expression of Beclin-1 mRNA and the Beclin-1 protein also increased in lung tissues, while the level of 62 mRNA and the expression of P62 protein decreased ( <0.05). After Apelin-13 intervention, the above indexes were all improved ( <0.05, compared with the Model group). unassigned: Exogenous Apelin has a certain preventive and therapeutic effect on the formation of PAH, and the mechanism may be related to its inhibition effect on autophagy.