Aim To investigate the serum plasminogen activator inhibitor-1 (PAI-1) level in patients with obstructive sleep apnea hypopnea syndrome (OSAHS) and its correlation with carotid intima-media thickness(CIMT) and plaque stability. Methods 167 patients who underwent polysomnography (PSG) in Baoji Municipal Central Hospital from July 2019 to January 2021 were enrolled and divided into control group (n＝46), mild OSAHS group (n＝15), moderate OSAHS group (n＝39), and severe OSAHS group (n＝67) according to sleep apnea-hypopnea index (AHI). Clinical data, PSG-related indexes, blood biochemical indicators, serum PAI-1 level, and CIMT were compared in the three groups. The relationship between CIMT and serum PAI-1 concentration in OSAHS patients was analyzed. According to CIMT, carotid plaque morphology, and ultrasonographic features, OSAHS patients were divided into simple OSAHS group (n＝37), OSAHS stable plaque group (n＝46), and OSAHS unstable plaque group (n＝38). PAI-1 level in each group was compared. Multivariate Logistic regression analysis was used to explore the risk factors of carotid plaque stability in OSAHS patients. Results There were statistically significant differences between the four groups regarding sex, body mass index (BMI), hypertension, smoking history, AHI, oxygen depletion index (ODI), oxygen saturation less than 90% of the time in sleeping time (Ts90%), the lowest nocturnal oxygen saturation (L-SaO₂), CIMT and serum PAI-1 level (P＜0.05). Pearson correlation analysis showed that CIMT was positively correlated with PAI-1 level in OSAHS patients (r＝0.675,P＜0.001). The level of PAI-1 in the simple OSAHS group was 1.20 times, in the OSAHS stable plaque group was 1.79 times, and in the OSAHS unstable plaque group was 2.01 times that of the control group, and the difference had statistical significance (all P＜0.05). Multiple linear regression suggested that CIMT was independently associated with AHI (B＝0.019, P＝0.001), PAI-1 (B＝0.012, P＜0.001), and low density lipoprotein cholesterol (LDLC)(B＝0.081, P＝0.028) after calibrating confounders. Multivariate Logistic regression analysis showed that after calibrating confounders, hypertension (OR=4.1,5%CI:2.034～18.117), diabetes (OR=1.0,5%CI:1.158～3.645), PAI-1 level (OR=1.1,5%CI:1.039～1.145), moderate OSAHS (OR=1.7,5%CI:1.162～3.730), severe OSAHS (OR=5.4,5%CI:1.085～31.370) were independent risk factors for unstable carotid plaque in patients with OSAHS (P＜0.05). Conclusion The level of PAI-1 might increase gradually accompanied by the severity of OSAHS and the level of PAI-1 might be positively correlated with CIMT. PAI-1 might be an independent risk factor for unstable arterial plaque in OSAHS.