This experiment aimed to obtain the relative depth of the porous and the average aperture of the paper surface and investigate the relationship of the porous relative depth and the average aperture with the paper surface characteristics. The IGT printability tester was used to simulate the offset printing approach to do printing on three kinds of brown paper. The Image J image processing method was used to quantitatively analyze the scanning electron microscopy (SEM) image of printing surface of five kinds of non-coated paper. The results showed that the porous relative depths were between 107 and 133, and the average apertures were between 36.06 μm and 45.71 μm. The shallower the porous relative depth was, the higher the smoothness of paper surface would be, vice versa; the smaller the average aperture was, the higher the glossiness of paper would be, vice versa. In conclusion, the method of image processing can quickly and efficiently determine the roughness and the reflection of incident light of paper surface. Under the case of little difference of average aperture, the smaller the value was, the higher the density, saturation, glossiness of the offset printing image were. But if the average aperture was too small, the particle of the ink can not permeate to the porous successfully. Given that, the abrasion resistance of the image would be disappointing.