Objective To explore the safety and feasibility of starting 6 Minute Walking Test （6MWT） in advance for acute Myocardial Infarction (MI) patients in phase I cardiac rehabilitation after PCI. Methods Totally 69 acute MI patients in phase I cardiac rehabilitation after PCI were randomized into a control group （34 cases） and an interventiongroup （35 cases）.The control group conducted 6MWT at 1 day before discharge, while the intervention group started 6MWT at 4 days after PCI. The 6 Minute Walk Distance (6MWD), Heart Rate （HR） , Blood Pressure （BP） , blood oxygen saturation, BORG score and cardiac arrhythmia rate between the two groups during the test were compared. Results Both of the two groups completed the 6MWT.There were no significant differences in 6MWD, HR, blood oxygen saturation, Oxygenation, BORG score and cardiac arrhythmia rate between the two groups (P＞0.05 for all) . Conclusion Acute MI patients in phase I cardiac rehabilitation after PCI starting 6MWT at 4 days after PCI is safe and feasible. It can evaluate the effect of phase I cardiac rehabilitation and patients′ exercise ability, and help patients better understand self-training methods before discharge, then improve theirexercise endurance.