Objective　To offer the data for diagnosis and treatment of impingement of acromion. Methods (1)  the shoulder joints from fifteen female specimens were used for sectional dissection ;(2) subacromial fat pad from ten female specimens  were observed by MRI technology. Results (1) The subacromial fat pad was adjacent to deltoid bursa at subacromial region; the trapezius muscle was supeior to it, while the supraspinatus is inferior to it. It was square in cross section and is narrowly elongated in the oblique sagittal section and coronal section;the length and width of the subacromial fat pad is (48.91±7.5)mm and (28±4.7) mm, respectively. The thickness was (11.5±1.9 )mm in the central supraspinatus and ( 3.1±0.8)mm at acromial margin.(2)The subacromial fat pad could be clearly displayed by MRI in transverse, oblique sagittal, oblique coronal planes.The length of subacromial fat pad is (49.8±7.0)mm and the width is( 28.7±5.2)mm; the thickness is (12.5±1.5)mm at the central supraspinatus and (3.2±0.8)mm at acromial margin. (3) The data from direct anatomical observation and MRI observation of sectional subacromial fat pad showed no differences (P>0.05) in the length, width and thickness, respectively.    Conclusion    The measurement of the subacromial fat pad detected by MRI can provide an early diagnosis for acromial impingement syndrome.