In order to reveal the effect of gloss on color-difference evaluation,the printed samples are prepared by ink jet printer on matte,semi-gloss,gloss three papers with different gloss levels at the 5 basic international commission on illumination (CIE) color centers. About 1100 pairs of samples are carried out by 23 observers with normal color vision based on the psychophysical method of pass-fail. The calculated CIELAB color difference shows that the color discrimination thresholds have no obvious difference for different gloss.The STRESS is 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,except the CIELAB,the others have no obvious discrepancy. For the optimized kL values,the higher gloss the smaller kL,which indicates that the lightness difference is more noticeable for the higher gloss printed samples for evaluating color difference.