〔Abstract〕 Objective To investigate the influence of acute myocardial infarction(AMI) combined with hypertension on its circadian rhythm. Methods A total of 1 006 cases of AMI who underwent emergency percutaneous coronary intervention(PCI) surgery were collected continuously, and they were divided into a combined hypertension group and a non-combined hypertension group according to whether it was combined with hypertension. The day was divided into 4 and 12 time periods in units of 6 hours and 2 hours, and the number of cases and differences between the two groups in each time period were compared. Results After propensity score matching(PSM), the two groups had different onsets in the 4 time periods of 0:00—5:59, 6:00—11:59, 12:00—17:59 and 18:00—23:59(P=0.014,0.045,0.035,0.016). After further subdividing the time into 12 time periods in units of 2 hours, the morning peak of the onset time of the hypertensive group was 10:00—11:59(P=0.004), and there was another peak at 2:00—3:59 in the morning(P=0.002). Multivariate Logistic regression indicated that compared with non-combined hypertension, AMI with hypertension had an increased risk of onset in the morning(6:00—11:59)(OR, 1.440; 95%CI, 1.089-1.904;P=0.011). Conclusion Hypertension affects the circadian rhythm of the onset of AMI and the peak time of onset, and it is a risk factor for the onset of AMI in the morning peak period(6:00—11:59).