Abstract: Objective: To observe the anatomical features of posterior arch of atlas in adult and provide the anatomical basis for its operation.Methods:The bony structures and vertebral artery groove of posterior arch of atlas in 80 adult dry atlas specimens were measured.Results:The inside and outside radius,height and thickness of posterior arch of atlas were(21.75 2.59) mm,(29.85 2.27) mm,(7.49 2.75) mm and(7.56 2.17) mm,respectively.The radians of medial and lateral margin of posterior arch of atlas were(83.4 4.4) and(75.2 4.2) degrees.The length,width,height and inclination angle of vertebral artery groove were(9.86 2.41),(5.67 1.54) and(1.79 0.24) mm and(16.8 2.71) degrees,respectively.The vertical axis angle,transverse foramen angle and lateral mass angle were (18.1 2.4) degrees,(20.7 2.5) degrees and(11.4 1.8) degrees.Conclusions:The anatomical data of bony structures and vertebral artery groove of posterior arch of atlas have certain guiding significance in the treatment of atlas fracture with screw fixation,which can avoid to damage the spinal cord and vertebral artery.