In order to reveal the effect of gloss on medium-small color difference evaluation, the printed samples were prepared by ink jet printer on matte, semi-gloss two papers with different gloss levels at the 5 basic CIE color centers. About 30 color samples were made on two kinds of paper; experiment of color difference was carried out by 20 observers with normal color vision based on the psychophysical method of comparison. The standardized residual sum of squares (STRESS) and F test were proposed to test the four classical color-difference formulae, CIELAB, CMC, CIE94, CIEDE2000 and CAM02 series CAM02-LCD,CAM02-SCD,CAM02-UCS. For the original color difference formulae, CIEDE2000 performed the best, and CIELAB color difference formulae performed the worst, while there′s still room for CIE94 for improvement. For the optimized kL values, the higher gloss is, the smaller kL is, which indicated that the lightness difference are more noticeable for the higher gloss printed samples for evaluating color difference.