Objective To study the relationship between sleep apnea hypopnea syndrome （SAHS） and the severity of vertigo in middle-aged and elderly patients with unexplained vertigo. Methods The middleaged and elderly patients with unexplained vertigo in Shantou Central Hospital or Nanao Branch Hospital from January 2019 to December 2020 were enrolled and were classified into four groups according to their clinical symptoms and results of polysomnography： non SAHS group， mild SAHS group， moderate SAHS group and severe SAHS group. The clinical characteristics of the four groups were compared. The relationship between apnea hypopnea index （AHI）， minimum nocturnal saturation of peripheral oxygen （SpO2 ）， the severity of SAHS， Pittsburgh Sleep Quality Index （PSQI） score and Dizziness Handicap Inventory （DHI） score were analyzed. Multivariate linear regression was used to explore the independent factors of DHI score. Results A total of 120 middle-aged and elderly patients with unexplained vertigo were enrolled， including 45 patients without SAHS， 26 patients with mild SAHS， 28 patients with moderate SAHS and 21 patients with severe SAHS. Expect for gender ratio， prevalence of hypertension， total cholesterol and low density lipoprotein cholesterol， there were significant differences in body mass index （BMI）， AHI， minimum nocturnal SpO2， DHI score and other characteristics among the four groups （P＜ 0.05）. The DHI score was positively correlated with AHI （r=0.896， P＜ 0.001）， the severity of SAHS （r=0.858， P＜ 0.001） and PSQI score （r=0.813， P＜ 0.001）， and negatively correlated with minimum nocturnal SpO2 （r=-0.775， P＜ 0.001）. Multivariate linear regression showed that BMI （β=2.012， P＜0.001）， triglyceride （β=1.771， P=0.001）， diabetes （β=3.243， P=0.032） and the severity of SAHS （β=4.398， P＜ 0.001） were independent factors of DHI score. Conclusions There was a relationship between SAHS and the severity of vertigo in middle-aged and elderly patients with unexplained vertigo.