Abstract: Objective To examine the relationship of daytime and nighttime blood pressure variability（BPV）with carotid atherosclerosis in patients with hypertension and type 2diabetes,and to provide a foundation for optimizing the treatment. Methods A total of 163 patients with essential hypertension（EH）were divided into hypertension with diabetes mellitus group（EH+DM,n=65）and hypertension group（EH,n=98）. A total of 35 diabetes mellitus patients with normal blood pressure were enrolled as DM group and 50 healthy individuals as normal control group（N group）. All subjects received 24 hour ambulatory blood pressure monitoring and neck vascular ultrasound examination. BPV indexes included both standard deviation and variation coefficient of blood pressure. Results Using standard deviation as BPV index:daytime systolic blood pressure standard deviation（dSSD）and diastolic blood pressure standard deviation（dDSD）,nighttime systolic blood pressure standard deviation（nSSD）in EH+DM,EH and DM group were significantly higher than N group（all P＜0.05）. Compared with EH group,EH+DM group’s nSSD （13.3±2.9）vs（10.5±2.3）mm Hg,nighttime diastolic blood pressure standard deviation（nDSD）（10.7±2.2）vs（8.4±2.0）mm Hgwere higher. Using blood pressure variation coefficient as BPV index:compared with the N group,EH+DM group’s daytime systolic blood pressure variation coefficient（dSCV）and diastolic blood pressure variation coefficient（dDCV）,nighttime systolic blood pressure variation coefficient（nSCV）and diastolic blood pressure variation coefficient（nDCV）were significantly increased（all P＜0.05）. Compared with N group,DM group’s dDCV （12.1±1.9）% vs（10.8±2.0）%,P＜0.05was higher. EH+DM group’s dSCV（10.7±2.5）% vs（8.5±1.8）%and nSCV （9.8±1.6）% vs（8.0±1.7）%were increased（both P＜0.05）when compared with EH group. In addition,DM and EH+DM group’s incidence of non-dipper type blood pressure（68.6% and 69.2%）were significantly higher than EH and N group（43.9% and 42.0%）,all P＜0.01. The neck vascular ultrasound examination showed that EH,DM,EH+DM group’s abnormal carotid intima-media thickness（IMT）detection rate were higher than N group（60.2%,77.1%,84.6% vs 24.0%,all P＜0.01）. And detection rate of carotid IMT abnormalities in male was higher than female（73.6% vs 45.2%,P＜0.05）. The detection rate of abnormal carotid IMT in non-dipper type group was higher than dipper type group（74.4% vs 47.0%,P＜0.01）. Multivariate analysis showed that male,nSSD and nSCV were related with IMT（B=0.491,0.582,0.637,respectively,all P＜0.05）. Conclusion In patients with hypertension and type 2diabetes,the daytime and nighttime BPV,the detection rate of non-dipper type blood pressure increased significantly,blood pressure circadian rhythm disorder happened more frequently and the detection rate of abnormal carotid artery intima is also higher with more in male patients.