Based on the scanner and STFI-Mottling Expert testing software, a new method using the COVM (modified coefficient of variation) to characterize the print mottle of papers was introduced. The print mottle image on paper surface was acquired through a scanner, and then studied from the perspective of digital image processing through software analysis. The experiment selected newspaper, offset paper, coated paper and inkjet paper to analyze print mottle in different wavelength ranges and different orientations. The method using the modified COVM proposed in this paper could effectively detect printing mottle. The correlation with visual judgment was better than that of traditional methods using the COVM to characterize the print mottle of papers. There were also some advantages in detecting the print mottle within different wavelength ranges and orientations of mottle. In conclusion, the new method is simpler and more objective as compared to the traditional method. It is more convenient to solve the problems caused by print mottle, and then improve the printing quality.