Objective To analyze the distribution of corneal surface Q-value in children without ammetropia calculated by tangential radius.Methods It was a cross-sectional study.The corneal topography of 65 eyes from 33 emmetropic children was examined by Obscan-Ⅱ and the tangential curvature data was guided by computer.The distance between two adjacent data points was 0.1 mm for all 360 semi-meridians within 4.5 mm of the corneal vertex.The Q-values of the 360 semi-meridians were calculated by the tangential radius from the tangential map based on a conic mathematical formula and linear regression method.Data were analyzed with a paired t test.Results The result of Q-value analysis showed that the 15° region in the Q-value distribution of the samples in both right and left eyes was normal.Negative values from all sections of the corneal surface show the prolate shape.The Q-value distribution of the four 15° regions was as follows:for right eyes:nasal (33 eyes) -0.3659±0.1064,temporal (31 eyes) -0.2456±0.1015,superior (28 eyes) -0.2786±0.0813,inferior (19 eyes) -0.2059±0.0704; for left eyes:nasal (32 eyes) -0.4529±0.1327,temporal (27 eyes) -0.2249±0.0907,superior (26 eyes) -0.2939±0.0704,inferior (18 eyes) -0.2321±0.0849.Conclusion This study reveals the shape of the corneal surface of emmetropic children.The 15° region Q-values of both right and left eyes become gradually less negative in order from the nasal,superior,temporal to inferior regions.