Abstract： Objective To evaluate the structure and stiffness of the common carotid artery (CCA) in patients with obstructive sleep apnea syndrome (OSAS) by RFQIMT and RFQAS technology and analyze the relationships between the parameters of CCA and cardiovascular risk factors.Methods 113 participants with habitual snoring suspected OSAS were divided into control group,mild,moderate and severe OSAS groups according to apnea hypopnea index(AHI)＜5,5-20,20-40,＞40 event/hour respectively.Carotid parameters included intima-media thickness (IMT),diameter (D),distension (Dis),distensibility coefficient (DC),compliance coefficient (CC),pulse wave velocity (PWV),stiffness index α and β were collected by RFQIMT and RFQAS.Multivariate linear regression analysis was applied to analyze the relationships between CCA parameters and cardiovascular risk factors.Results ①The clinical characteristics:blood pressure had significant difference among the four groups (P ＜0.05).SO2,SO2 min decreased and T90,ODI increased significantly in mild,moderate and severe group (P ＜0.05).②The structure parameters of CCA:IMT,D and plaques had no significant difference among the four groups (P ＞0.05).③The elasticity parameters of CCA:Compared with control group,Dis increased significantly in mild group (P ＜0.05).PWV,α,β increased significantly in moderate group (P ＜ 0.05).Compared with mild group,PWV,α,β increased significantly in moderate group (P ＜0.05).Compared with moderate group,α,β increased significantly in severe group (P ＜0.05).④By multivariate linear regression analysis,age was an independent predictor of IMT,Dis,D,CC,PWV,α,β(P ＜0.05).A blunted nocturnal fall was an independent predictor of D,DC,CC,PWV (P ＜0.05),SBP,DBP and PP of daytime had an important effect on D (P ＜0.05).SO2 was independently correlated with PWV (P ＜0.05).PP was an independent predictor of PWV,α,β (P ＜0.05).Smoking was an independent predictor of plaque (P ＜0.05).Conclusions ①Stiffness is damaged earlier than morphology of CCA in patient with OSAS.②PP,a blunted nocturnal fall and SO2 are correlated with stiffness of CCA significantly.It indicates that abnormal circadian blood pressure rhythm and hypoxia are associated significantly with stiffness of CCA in patient with OSAS.