Based on the scanning electron microscope(SEM) images taken from the mortar anchor corrosion experiment, we extracted the mortar anchors' microscopic morphology characteristics by image processing technology first, and quantitatively described the morphology characteristics by fractal theory. Then the relationship between the fractal dimension and the macroscopic bond strength of mortar anchor was established. Finally, the mercury intrusion test was applied to analyze the results of SEM image processing. The results show that, as the corrosion time gets longer, the anchor's porosities under both force conditions and non-force conditions linearly increase, but the pore number and the pore fractal dimension gradually reduce, and the relationship between fractal dimension and porosity is almost negatively linear. As the fractal dimension decreases, the bond strength of mortar anchor increases first, and then decreases. The results comparison of mercury intrusion test and the image processing shows that the inaccuracy is within the range of 5% to 7%.