Aim To investigate the protective effect of olmesartan on vascular endothelial function in patients with hypertension complicated with coronary heart disease and diabetes mellitus, by observing the change of vascular endothelial function before and after treatment with olmesartan. Methods 160 cases of hypertensive patients were collected, and according to whether complicated with coronary heart disease and diabetes mellitus, the patients were divided into 3 groups:pure hypertension group (H group, n＝40), hypertension complicated with coronary heart disease group (HC group, n＝62) and hypertension complicated with coronary heart disease and diabetes mellitus group (HCD group, n＝58). And then each group was divided into 2 subgroups:olmesartan intervention subgroup (A subgroup) and and non olmesartan intervention subgroup (B subgroup). Baseline data and general examination indicators of each group were counted. Enzyme-linked immunosorbent assay was used to detect the concentration of serum nitric oxide (NO) and endothelin-1 (ET-1). The number of peripheral blood endothelial progenitor cell (EPC) was detected by flow cytometry.Above indicators were reexamined after intervention with olmesartan for 3 months. Results (1)Vascular endothelial relaxing and contracting factors:Before treatment, compared with H group, NO concentration was significantly lower, while ET-1 concentration was significantly increased in HC group and HCD group, and the change of HCD group was more obvious (P＜0.05). After treatment, compared with before treatment, NO concentration was significantly increased, while ET-1 concentration was decreased in HC-A subgroup and HCD-A subgroup (P＜0.05). (2) EPC number of peripheral blood:Before treatment, compared with H group, the EPC number of peripheral blood was significantly decreased in HC group and HCD group, and the decrease of HCD group was more obvious (P＜0.05). After treatment, compared with before treatment, the number of EPC was significantly increased in HC-A subgroup and HCD-A subgroup (P＜0.05). Conclusions Hypertensive patients complicated with coronary heart disease and diabetes mellitus will increase the damage of vascular endothelium. Olmesartan can inhibit the imbalance of vascular endothelial relaxing and contracting factors, increase the EPC number of peripheral blood, and it has protective effect to vascular endothelium.