This experiment studied the print mottle of ink-jet papers by combining the scanner and the STFI-Mottling Expert testing software. From the perspective of digital image processing, the mottle testing software based on the STFI print mottle prediction model was adopted. Two kinds of coated paper and two kinds of offset paper were selected to test the print mottle of single color solid print in order to study the print mottle of different ink-jet papers. The print mottle of blank offset papers was more serious than that of the coated papers. The print mottle of cyan, magenta, and yellow color solid print for four kinds of paper was consistent with the test results of blank papers, but the result of black color solid print was special. Human eyes are very sensitive to the print mottle with the wavelength of 2~16 mm. The mottle values tested by the STFI-mottling expert software had a good correlation with the human visual judgment, and the correlation coefficient was 0.90. The study on the print mottle of ink-jet papers with the STFI print mottle prediction model has certain significance in guidance of the actual production.