Abstract: Objective To study the effect of obstructive sleep apnea-hypopnea syndrome （OSAHS） on diurnal blood pressure and cardiac arrhythmias in patients of hypertension. Methods Eighty-six patients with hypertension complicated with OSAHS （HT+OSAHS group） and 30 patients with hypertension without OSAHS （HT group）and 30 healthy persons （N group） were enrolled. All subjects in 3 groups underwent polysomnography（PSG）, ambulatory blood pressure, ambulatory electrocardiogram and echocardiography. Results The night average systolic and diastolic blood pressure （SBP and DBP）are higher in HT+OSAHS group than that in HT gronp and N group. Non-dipper has been found in 61.4% in HT+OSAHS group while is markedly higher than that in HT group（21.2%） and N group（1.8%） . Prevalence rates of arrhythmias are significantly higher in HT+OSAHS group than that in comparative group, while left ventricular ejection fraction（LVEF） is lower （P＜0.05） .Conclusion OSAHS has been shown to have significant deteriorative effect on diurnal blood pressure, arrhythmias and cardial function in patients of hypertension.