Objective To investigate the trends of proportion and in-hospital mortality of patients with ST-segment elevation myocardial infarction (STEMI) or non-ST-segment elevation myocardial infarction (NSTEMI) over the past 12 years. Methods A retrospective analysis was performed on 4 868 patients, who were hospitalized for acute myocardial infarction (AMI) in the Department of Cardiovasology, Changhai Hospital, Naval Medical University (Second Military Medical University) from Jan. 1, 2007 to Dec. 31, 2018. The annual percentage change (APC) method was used to analyze the changes of the proportion and in-hospital mortality of STEMI and NSTEMI patients. Results Of the 4 868 AMI patients, 3 064 (62.9%) had STEMI and 1 804 (37.1%) had NSTEMI. The proportion of NSTEMI patients significantly increased within the 12 years (APC value 14.0%, P<0.01), from 15.7% in 2007 to 45.2% in 2018; the proportion of STEMI patients showed a significant decline (APC value -5.5%, P<0.01), from 84.3% in 2007 to 54.8% in 2018. The in-hospital mortality of AMI patients showed a significantly downward trend (APC value -6.6%, P<0.05), from 7.0% in 2007 to 4.3% in 2018. The in-hospital mortality of NSTEMI patients also showed a significant decline (APC value -11.9%, P<0.05), from 13.9% in 2007 to 1.9% in 2018, while that of STEMI patients showed no significant change (APC value -3.8%, P=0.225). Conclusion Among AMI patients in our hospital from 2007 to 2018, the proportion of NSTEMI patients showed an increasing trend. The in-hospital mortality of NSTEMI patients decreased within the 12 years, while that of STEMI patients did not.