Objective To investigate the apoptosis of peripheral blood circulating endothelial cells (CECs) and the expression of ACE2 and Mas protein in patients with acute pulmonary embolism (APE) before and after treatment. Methods A total of 82 patients with APE received by the emergency department of our hospital were collected and divided into medium-high risk group (n=42) and low risk group (n=40) according to the severity of the disease. Forty healthy subjects who underwent physical examination in our hospital were selected as the control group. Peripheral blood of APE patients at admission, discharge and healthy subjects was taken. Flow cytometry was used to analyze the number of CECs, and their apoptosis level and surface angiotensin converting enzyme 2 (ACE2) expression in peripheral blood of APE patients and healthy subjects. Western blotting was used to detect the levels of apoptotic proteins Bax, Bcl2, caspase 3/9 and the expression of proteins ACE2 and Mas in CECs. Results The number and apoptosis rate of CECs in peripheral blood of patients in the high-risk group and the low-risk group at admission were significantly higher than those in the control group, and the number and apoptosis rate of CECs in the high-risk group were significantly higher than those in the low-risk group (P＜0.05). The number and apoptosis rate of CECs in the high-risk group and the low-risk group at discharge were significantly lower than those at admission (P＜0.05). The levels of Bcl2 protein, Bcl2/Bax protein ratio and cleaved caspase 3/9 protein in CECs of patients in the middle-high-risk group and low-risk group at admission were significantly higher than those in the control group, and the levels of these indexes in the middle-high-risk group were significantly higher than those in the low-risk group. At the same time, the levels of the above indexes in CECs of patients in the middle-high-risk group and low-risk group at discharge were significantly lower than those at admission (P＜0.05). It was further found that the levels of ACE2 and Mas in CECs of the middle-high risk group and the low-risk group were significantly lower than those of the control group at admission, and the levels of the above indexes in the middle-high risk group were significantly lower than those in the low-risk group (P＜0.05). Conclusion The number and apoptosis rate of CECs in peripheral blood of patients with APE increased significantly, and the number and apoptosis rate of CECs decreased after treatment, suggesting that CECs may be related to the pathogenesis and prognosis of APE, and the ACE2-Mas axis may be involved in the regulation of CECs apoptosis