Objective To investigate the effects of ischemic postconditioning (IPOC) on myocardial perfusion and prognosis in patients with acute ST-segment elevation myocardial infarction (STEMI) who were treated with emergency percutaneous coronary intervention (PCI). Methods A total of 203 patients with STEMI who received emergency PCI were randomly divided into IPOC group (n=103) and control group (n=100). For the patients of IPOC group the angioplasty balloon was re-inflated within one minute after the beginning of reperfusion, the procedure was repeated three times, each time the inflation of balloon lasted for 1 minute using low-pressure (4-6 atm), and the interval between the inflation procedures was one minute. For the patients of the control group , no additional intervention was employed during the first 6 minutes of reperfusion. Cardiac troponin I(cTnI) peaks, creatine kinase-MB (CK-MB) peaks, left ventricular ejection fraction (LVEF), wall motion score index (WMSI), corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC), and major adverse cardiac events (MACE) occurred during hospitalization time in both groups were recorded and the results were compared between the two groups. Results No significant differences in age, sex, risk factors, infarction-related artery, ischemia time, etc. existed between the two groups (P>0.05). The CTFC values of IPOC group were significantly faster than those of the control group, that was (25.3±7.9) vs.(29.4±8.4),(P<0.05). The CK-MB peak and cTnI peak values of IPOC group were remarkably lower than those of the control group, those were (157.3 ±83.6) U/L vs. (201.5 ±77.3) U/L and (2.5 ±1.3) ng/mL vs. (3.1 ±1.0) ng/mL respectively (P<0.05). At the time of admission, there were no significantly differences in the LVEF and WMSI values between the two groups, and three months after PCI the LVEF and WMSI values of IPOC group were significantly better than those of the control group, those were (57.4 ±8.7)% vs. (53.6 ±9.3)% and (1.19 ±0.4) vs. (1.27 ±0.3) respectively, the differences were statistically significant (P<0.05). Three months after PCI, the occurrence of MACE in IPOC group was obviously lower than that in the control group (P<0.05). Conclusion Ischemic postconditioning can improve the infarction-related artery blood flow in patients with STEMI who receive emergency PCI treatment, it can also reduce ischemia-reperfusion injury and improve the cardiac function as well as patient’s prognosis after AMI.