Abstract： Objective To study the impact of primary PCI in culprit artery on epicardial blood flow of nonculprit artery in patients with STEMI. Methods Enrolled 117 patients with anterior wall STEMI were treated with primary PCI in the culprit artery, left anterior descending artery (LAD, as study group.Another 100 patients with normal coronary artery evidenced by angiography were enrolled as control group.The differences in CTFC (corrected TIMI frame count measured by using digital subtraction arteriography,TIMI =thrombolysis in myocardial infarction) and MBG (myocardium blood flow perfusion grading)between pre and post primary PCI in both culprit artery and nonculprit artery ( left circumflex artery, LCX),and CTFC and MBG were also detected in the subjects of control group. Blood samples were collected and the levels of CRP (C-reactive protein) were assayed. Clinical and angiographic features were analyzed.Results The CTFC of nonculprit artery (LCX) and the level of MBG in patients with anterior wall STEMI were different from the level of MBG and CTFC in control group ( P＜0. 05) before primary PCI. The level of MBG and CTFC in nonculprit artery (LCX) were improved (P ＜ 0. 05 ) after primary PCI, but they did not resume to normal level. Patients without reflow in culprit artery had higher incidence of no reflow in nonculprit artery than patients with re-flow (78％ vs. 8％, P ＜ 0. 01 ), and the level of CRP in patients without reflow in nonculprit artery were higher than those in patients with re-flow ( P ＜ 0. 05). Conclusions The perfusion of nonculprit artery may be impaired in patients with STEMI. Although the perfusion of nonculprit artery may be improved after primary PCI in culprit artery, but it was still lower than those in the control group, and inflammation mechanism might contribute to it.