In order to study the human color vision characteristics, the just-noticeable color difference discrimination threshold experiment at the 17 basic CIE color centers with about 1000 pairs of samples was carried out by 16 observers with normal color vision on the CIE1976 a*-b* plane, by using reflective samples color stimuli based on the psychophysical method of constant stimuli. And the color discrimination thresholds were represented via chromaticity ellipses. The detailed processing and analysis of the experimental results indicate that the color discrimination characteristics of human eyes are different for individual color regions and directions in the a*-b* plane,and namely the CIE1976 a*-b* plane is visually non-uniform. The visual color tolerance in the third and fourth quadrants is smaller than the first and second quadrants, the biggest tolerance is in the region of high chroma orange, and the smallest is in blue.The visual color difference scale in the red-green direction is generally smaller than that in the yellow-blue one for the 17 CIE color centers. The experimental data provides references for the improvement of uniform color space and color-difference formula.