Objective To study the degree of stenosis of myocardial bridge- mural coronary artery (MB-MCA) by 128-slice spiral CT in systolic and diastolic phases and its clinic. Methods 117 patients with MB-MCA were retrospectively analyzed in this study. We recorded the position, type, degree of MB-MCA in systolic and diastolic phase, evaluated the difference of stenosis between different types and relationship between systolic stenosis and the incidence of atherosclerotic plaque in the proximal wall of the coronary artery. The relationship between the extent of diastolic stenosis of 58 patients with simple MBMCA and the clinical symptoms and Treadmill exercise test was evaluated. Results Among the 117 patients with MB-MCA, 29 cases had a systolic stenosis rate of ≥ 50% and 14 cases had a stenosis in the diastolic (P<0.05). In the 117 cases of MB-MCA, there were 46 cases of incomplete type and 71 cases of complete type. The stenosis was statistically significant in systolic and diastolic (P<0.05). MB-MCA had a higher rate of diastolic stenosis in patients with clinical manifestations and Treadmill exercise test positive rate. With the increase of systolic stenosis, the incidence of proximal atherosclerosis in MB-MCA increased (P<0.05). Conclusion MB-MCA have varying degrees of stenosis, the degree of stenosis was related to the type of MB-MCA in the systolic and diastolic phases. The higher degree of systolic stenosis of MCA, the more likely to occur at the proximal atherosclerotic plaque; stenosis of MB-MCA in diastolic can lead to coronary artery function changes.