Background and Purpose：As important components of lung tissue, endothelial cells (ECs) are associated with many lung diseases. The role of ECs dysfunction in idiopathic pulmonary fibrosis (IPF) and how to improve alveolar capillary barrier (ACB) to treat IPF is incompletely understood. Therefore we investigated the involvment of endothelial Sphingosine-1-phosphate receptor 1 (S1pr1) in PF and therapeutic effect of selective S1pr1 agonist IMMH002. Experimental approach：Databases of IPF patients and individuals without fibrosis were mined by Seurat. We generated an endothelial-conditional S1pr1 knockout (S1pr1+/−) mice and we also examined a bleomycin-induced model of pulmonary fibrosis (PF). We performed qRT-PCR,Western blot, Immunofluorescence staining and EC permeability experiments. Key results：Expression of S1pr1 in ECs was reduced markedly in IPF patients. Mice with endothelial-specific S1pr1 deficiency exhibited severer inflammation and fibrosis upon challenge with bleomycin. Significant accumulation of alpha-smooth muscle actin (α-SMA) was observed near vessels after S1pr1 deficiency, which indicated a potential connection between ACB injury and fibrosis. S1pr1 activation by a selective agonist IMMH002 could ameliorate PF by improving tight junctions in ECs and protects the ACB. Conclusion and Implications: Our results suggest that S1pr1 plays a significant role in ACB and it could be a potential target for IPF. Activation of S1pr1 with IMMH002 elicits a potent therapeutic effect in bleomycin-induced fibrosis by increasing tight junctions in endothelial cells and protecting the integrity of ACB therefore improve survial rate and lung function.