Objective To investigate the change of ambulatory blood-pressure in elderly hypertension patients combined with moderate to severe obstructive sleep apnea-hypopnea syndrome(OSAHS) and to explore the effect of OSAHS on the development of cardio-cerebrovascular diseases.Methods Seventy-two patients were divided into study group(moderate to severe OSAHS combined with hypertension,n=36,average age=(68±23.3) years,BMI=(27.7±2.3) kg/m2)and control group(hypertension without,n=36,average age=(64±18.5) years,BMI=(26.8±1.8) kg/m2),according to the clinical blood pressure,ambulatory blood pressure and polysomnogram.To compare the effect of different degree of OSAHS on the diurnal blood pressure between the two groups.Results There was no significant difference between these two groups in average age,gender and BMI.For the study group,the nocturnal systolic pressure was(143.2 ±10.7)mmHg,the ratio of non-dipper hypertension was 83.3%,and the morning systolic pressure was(146.9±16.1)mmHg.For the control group,the nocturnal systolic pressure was(132.2 ±13.1)mmHg,the ratio of non-dipper hypertension was 27.5%,and the morning systolic pressure was(137.2±20.1)mmHg.There was significant difference between these two groups.The data of study group were much higher than those of the control group.Conclusion Moderate to severe OSAHS can affect circadian rhythm of blood pressure.