【Objective】To explore the association between blood pressure and the plasma levels of renin，angiotensin Ⅱ and aldosterone in hypertensive patients with different degrees of obstructive sleep apnea syndrome（OSAS）.【Methods】Patients with secondary hypertension，NYHA Ⅱ-Ⅳ heart failure，and stopping drugs which can affect renin- angiotensin-aldosterone system（RASS）for less than 1 month were excluded. Patients who were initially diagnosed as hypertension and completed polysomnography were conducted in the Third Affiliated Hospital of Sun Yat-sen University from November 2018 to December 2019. Apnea- Hypopnea Index（AHI）represents the severity of OSAS. Patients were measured plasma levels of renin concentration，angiotensin Ⅱ and aldosterone in supine positions. Blood pressure before therapy was also recorded. Subjects were divided into two groups based on AHI. Group A included no or mild OSAS patients with AHI < 15 and Group B included moderate or severe OSAS patients with AHI ≥ 15. The above indicators were compared between the two groups. We also tried to find the correlation of OSAS，blood pressure and RASS by linear correlation and multiple linear regressions.【Results】Positive correlations were found between AHI and aldosterone（rs= 0.215，P=0.011），AHI and plasma renin concentration（rs=0.233，P=0.006），AHI and ANG Ⅱ（rs=0.138，P=0.004）， AHI and systolic blood pressure（rs=0.306 ，P<0.001），AHI and mean arterial blood pressure（rs=0.263 ，P=0.002）， systolic blood pressure and plasma renin concentration（rs=0.288，P=0.001），diastolic blood pressure and plasma renin concentration（rs=0.213，P=0.012）. After adjusting for other variables，aldosterone was also significantly associated with AHI（β =0.160 ，P=0.035）.【Conclusions】OSAS severity is related to RASS ，especially to aldosterone. OSAS mainly affects systolic blood pressure and mean arterial blood pressure. Aldosterone receptor antagonist may be more available for hypertensive patients with OSAS.