Samples of undisturbed soil core were collected, 3 each, from a shrub patch and a grass patch in a tract of degraded sandy grassland encroached by shrub, Caragana microphylla Lam, in Taibus Banner of Inner Mongolia. Analysis of soil porosity is based on CT scanning and Fiji software. we analyze the pore parameters (such as porosity & equivalent diameter) with matlab based on 2D section images in every slice, and obtain trends of variations of pore parameters with depth. In additon, we can realize 3-D visualization of pores network with Fiji and qualitative description of soil pore distribution. Results show that shrub encroachment affected soil porosity and pore structure significantly. As a result, the soil in the shrub patch was much higher than that in the grass patch in total number of soil pores, number of macrospores (>1 000 μm), total porosity, macroporosity, and mean of equivalent pore diameter, and especially in mean macroporosity, the former was 3 times as high as the latter. In the grass patch, macropores were distributed mainly in the 0~50 mm soil layer, while in the shrub patch, they were found throughout the 0~400 mm soil layer, which is closely related to the well-developed root system of the shrubs.