Objective To assess retinal vessel caliber using computer-assisted software; to study clinical reliability and consistency between different reasearchers. Methods In this cross-sectional study, the retinal vessel diameters of 100 fundus pictures of children aged from 4 to 8 years were measured independently by 4 researchers using IVAN (University of Wisconsin, Madison, WI) computer-assisted quantitative assessment software. The arteriolar/venular caliber was measured and the ratio was calculated with the semi-automated software. Intraclass correlation coeffient were calculated to assess agreement between different researchers. Kappa test analysis was performed to assess agreement between new researchers and skilled researcher. Bland-Altman plots were drawed. Results Analysis of the retinal arteriolar and venular can be performed and reproduced on routine retinal photographs. The mean central retinal arteriolar (CRAE) measurements by the 4 researchers were 121.14±17.03, 120.40±17.68, 120.45±17.61, 120.79±19.05; the ICC value was 0.943(0.923-0.960). The mean central retinal venular equivalents (CRVE) were 181.66±29.33, 181.55±29.31, 181.23±30.12, 181.53±31.46; the ICC value was 0.939(0.917-0.956). The mean arteriolar/venular measurements were 0.67±0.06, 0.66±0.07, 0.67±0.06, 0.67±0.06; the ICC was 0.685(0.625-0.715). The Kappa values of CRAE were 0.702, 0.745 and 0.744, respectively; the values of CRVE were 0.822, 0.860 and 0.860, respectively; the values of the arteriolar/venular were 0.753, 0.604 and 0.601. Conclusion Retinal vessel measurements with IVAN software are reliable early in life. It can be helpful for future retinal vessel caliber assessment from a young age.