Objective To evaluate the asphericity of the anterior and posterior comeal surfaces in myopic eyes with different corneal diameters.Methods It was a cross-sectional study.One hundred and sixteen eyes of 116 myopic or myopic astigmatism patients were enrolled.The preo perative spherical refraction was -1.25～-10.75 D,and the cyclindrical refraction was 0.00～-3.50 D.The Q-value and spherical aberration of the anterior and posterior corneal surfaces for different corneal diameters (6,7,8,9 mm) were measured with a Pentacam.The correlations between Q-value and spherical aberration,corneal refraction and central corneal thickness were investigated usiug a Pearson correlation,and a linear regression was used to establish the regressione quation of Q-value and spherical abberration.Results The Q6 mm,Q7 mm,Q8 mm,Q9 mm of the anterior corneal surfaces of the 116 eyes were -0.24±0.09,-0.29±0.09,-0.33±0.09,-0.39±0.10,respectively; posterior corneal surfaces were -0.12±0.12,-0.21±0.11,-0.30±0.10,-0.38±0.10,respectively.The Q-values of the anterior corneal surfaces were more negative than the posterior corneal surfaces,the differences were significant except the 9 mm (t=-10.35,-6.68,-3.46,P＜0.01).Positive relationships were found between the Q-value of anterior and posterior corneal surfaces for 6-9 mm corneal diameters (r=0.30,0.37,0.40,0.42,P＜0.01).For a 6 mm corneal diameter,the regression equation of the anterior corneal surface was SA=0.663Q+0.415,and the posterior corneal surface was SA=0.159Q-0.177.Positive relationships were also found between the anterior Q-values and cyclinder refractions for 6-9 mm corneal diameters (r=0.28、0.27、0.25、0.22,P＜0.05).Negetive relationship were found between the posterior Q value and comeal thickness for 7-9 mm corneal diameter (r=-0.18,-0.21,-0.24,P＜0.05).ConcIusion Both the anterior and the posterior corneal surfaces in myopic eyes were prolate.As the corneal diameter increased,the Q-values became more negative.The relationship between Q-value and corneal spherical aberration can provide more valuable instructions for refractive surgeons when designing aspheric ablation.