Natural small molecules capable of activating endothelial nitric oxide synthase (eNOS) were selected, and their protective effects and mechanisms against hypertension-induced vascular endothelial cell injury were investigated. Molecular docking using Discovery Studio was performed to screen for natural compounds that bind to eNOS. The effects of the candidate compound 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PGG) were validated at the cellular and animal levels using a high-salt-induced human coronary artery endothelial cell (HCAEC) model and a C57BL/6J mouse model of high-salt diet-induced hypertension. The effects of PGG on eNOS phosphorylation at Ser1177, blood pressure, vasodilatory function and the intracellular nicotinamide adenine dinucleotide (oxidized form)/nicotinamide adenine dinucleotide (reduced form) (NAD⁺/NADH) ratio were examined. Molecular docking results revealed that PGG had high affinity for eNOS. In cell experiments, PGG significantly elevated the phosphorylation level of eNOS in endothelial cells in a high-salt environment. In animal experiments, PGG gavage (20 mg/kg for 35 days) significantly reduced systolic and diastolic blood pressure in hypertensive mice. Moreover, PGG increased the phosphorylation level of eNOS in aortic tissues and enhanced the endothelium-dependent diastolic function of aortic vasculature by elevating the NAD⁺/NADH ratio; however, an eNOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), blocked PGG-induced vasodilation. In conclusion, PGG improves vascular endothelial function and consequently reduces blood pressure in hypertensive mice by affecting eNOS phosphorylation. PGG provides a potential lead compound for targeted therapy of hypertension.