Objective: To investigate the diagnostic value of serum aldosterone to renin ratio (ARR) after captopril test for primary hyperaldosteronism (PHA). Methods: A total of 64 patients with PHA (a PHA group) and 37 patients with essential hypertension excluding PHA (a control group) admitted to First Affiliated Hospital of Hainan Medical College from January 2018 to December 2021 were selected as research subjects. All patients underwent captopril test. The baseline data, biochemical indexes, plasma renin concentration (PRC), plasma aldosterone concentration (PAC), PAC inhibition rate, and ARR after captopril test were compared between the 2 groups. The diagnostic value of different parameters for PHA after captopril test was analyzed by drawing the receiver operating characteristic (ROC) curve. Results: There was no difference in gender, age, body mass index, blood sodium, urine sodium, and urine potassium between the 2 groups (all P>0.05). The course of hypertension, systolic blood pressure, and diastolic blood pressure in the PHA group were significantly higher than those in the control group (all P<0.05), and the blood potassium level was significantly lower than that in the control group (P<0.05). After captopril test, the differences of PRC, PAC, PAC inhibition rate, and ARR between the PHA group and the control group were statistically significant (all P<0.05). The area under the ROC curve (AUC) of PRC, PAC, PAC inhibition rate, and ARR in the diagnosis of PHA were 0.642, 0.842, 0.858, and 0.947, respectively. The diagnostic value of ARR was the highest, followed by PAC and PAC inhibition rate, and the diagnostic value of PRC was lower. Conclusion: ARR after captopril test has high application value for PHA diagnosis.