ACEI and ARB dilate the small glomerular inlet and outlet arteries, but dilate the former to a greater extent than the latter, so that after drug administration. The perfusion pressure of the glomerulus decreases. In the long term, the above pharmacological effects help to protect glomerular function, especially for patients with diabetic nephropathy combined with hypertension, and ACEI and ARB are also the drugs of choice for such patients. However, it should be noted that if the blood creatinine is in the normal range before treatment, but it increases significantly after treatment, it is necessary to be alert to renal artery stenosis. The reason is that the renal blood supply is already insufficient in patients with renal artery stenosis, and the application of ACEI and ARB further decreases the glomerular perfusion pressure, and the renal function may deteriorate rapidly in a short time, even causing anuria. Therefore, patients with ACEI and ARB often need to monitor renal function closely, especially at the beginning of treatment.