Objective To compare the difference and accuracy of the two methods of calculation for the Q-value of corneal anterior surface that with tangential radius or sagittal radius. Methods Twenty-four aspheric test objects were manufactured with the Moore diamond turning lathe in this self-controlled study. The test objects were all verified by the TalySurf roughness profiler and the asphericity (Q) and vertex radius of curvature (r0) were fitted. Then, they were examined with the Orbscan Ⅱ corneal topography. The results were applied paired t-test and Bland-Altman figure to perform statistical analysis. Results ①The average r0-values of the horizontal semi-meridian calculated by the sagittal radius and the tangential radius were 7.72±0.09 mm, 7.73±0.09 mm. Both of them were close to but have statistical differences with the fitted value 7.70±0.08 mm. ②There was no statistical differences between Q-values of the horizontal semi-meridian calculated by the sagittal radius and the tangential radius and fitted value (sagittal refractive map: t=1.61, P>0.05; tangent refractive map: t=-0.87, P>0.05). ③The average differences between the Q-values of the horizontal semi-meridian calculated by the tangential radius and fetted values was more close to 0 than sagittal ones, and the 95% consistency limits of upper and lower range was smaller than sagittal ones. Conclusion Although the Q-values of corneal anterior surface calculated by tangential radius and sagittal radius are both reliable, the former is more accurate and stable.