Background Contrast sensitivity (CS) of amblyopia has been extensively studied,but its relationship with spatial frequency channels needs further research. Objective The purpose of this study was to investigate the reasons of the CS deficits in amblyopia through comparing the differences in CS between amblyopic and normal eyes from the point of view of spatial frequency channels. MethodsThe CS values of 166 normal children eyes and 143 amblyopic children abnormal eyes were measured by adopting OPTEC 6500.Then,spatial frequency channels' tuning curves were derived via principal component analysis and non-orthogonal rotation.Also,numbers and bandwidths of channels were calculated using the method of full width at half maximum ( FWHM ).All of these were used to analyze the variations of CS between amblyopia and normal eyes by comparing the numbers and the bandwidths of the channels.The reliability of spatial frequency channel was verified by a cross-validation study of 43 amblyopic children. ResultAt spatial frequency of 1.5,3.0,6.0,12.0,18.0 cpd,the mean of CS of amblyopia were 36.35±21.40,50.33 ± 33.46,46.88 ± 41.72,16.24 ± 17.26,4.67 ± 5.79,and the mean of CS of normal eyes were 49.49±24.69,87.23±40.87,93.18±51.99.36.63±24.72,15.70±13.87,with the rank-sum test results were H =27.83,66.61,68.34,78.23,89.88,P＜0.05.There existed three spatial frequency channels in both amblyopia and normal eyes.At the peaks of 3.0,6.0 and 12.0 cpd,the bandwidths of normal eyes were 1.03,1.02 and 0.99 octaves,and the bandwidths of amblyopia were 1.04,1.01and 0.73 octaves.Conclusions The reduction in bandwidths of the corresponding spatial frequency channels may cause the CS deficits in amblyopia.