Objective To provide the theoretical basis for slotting angle in double-door expansive laminoplasty of cervical spine and investigate the clinical significance by CT and measuring the associated parameters of laminar slotting angle on each segment of C2-7. Methods 87 male and 63 female cases of normal cervical-spine CT scanning result, aged from 27-62 with an average age of 42.35, were randomly selected during April 2015 to August 2015. Measured the ideal slotting angle and mini safety slotting angle of each segment of C2-7 by CT three-dimensional restruction software, on the central layer of laminar on cross section, a point from both lateral and medial cortex were selected respectively that are located at the junction of superior border of laminar and spinous process, and midpoint was selected from the connecting line of the 2 points. Another midpoint was selected in the same way from the junction of inferior border of laminar and zygopophysis. The connecting line by threading the 2 midpoints was the axis of laminar. Slotting point A was selected from the lateral cortex that is located at the junction of inferior zygopophysis and laminar, then slot at the axis which was perpendicular to laminar. The extension line of the groove was the ideal slotting angle line(X), and the angle between line X and median sagittal line(Y)was ideal slotting angle(α). On the thickest vertebral pedicle of each segment, made a tangent line(Z)of the most lateral border of canalis spinalis with the slotting point, then the angle(β)between line Z and Y was the mini safe slotting angle. Measured the ideal slotting angle α and the mini safe slotting angle β on bilateral of each segment of C2-7 accurated to 0.01°. Then group based on difference segment, lateral and gender to analyze the data measured. Results α on each segment of C2-7 were 42.37°±2.53° , 37.45°±3.36° , 37.20°±3.59°, 37.99°±2.99° , 37.78°±3.59° , 40.16°±2.41°, and β were 35.50°±1.21°, 14.83°±2.72°, 15.23°±2.94°, 15.18°±2.96°, 14.93°±2.29° and 20.16°±2.74°. The difference between C2 and C3-7 showed the statistical significance which also gone with the difference between C7 and C3-6. While the comparison between any 2 groups in C3-6 did not. α and β on different lateral did not show statistical significance. α of male was larger than female's which show the statistical significance; β on C7 of male was 20.68°±2.67° and female's was 18.67°±2.48°. The comparison between the 2 groups show statistical significance. Conclusion The slotting angle is larger than that of C3-7 when need to reduce the pressure of C2 segment in double-door expansive laminoplasty, slotting angle of the segment which needs pressure reduced should be measured by CT pre-operation to make an individualized surgical planning so as to reduce the surgical risk. Key words: Cervical spondylosis; Axis; Tomography