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In order to explore the mechanism of soil reinforcement and slope protection by plant roots, in this paper, the mechanical characteristics of roots on soil stabilization were discussed from the meso angle, and using a CT triaxial apparatus developed at the Yangtze River Scientific Research, a series of unconsolidated-undrained CT real-time triaxial shear test of the non-rooted clay sample and two kinds of Broussonetia papyrifera-rooted clay samples with different root diameters were carried out. Through a quantitative analysis of CT scan data of three sections at the different strain for three kinds of samples, it was found that both the downward section of (mean CT number) ME-ε1 curve and the upward section of (the variance of CT number) SD-ε1 curve of the non-rooted soils had a greater changing amplitude than those of the rooted soils in three different scan layer sections. It indicated that the internal defects of the rooted soil grew more slowly and weakly, the initiation and propagation of internal cracks slower, and the roots resist cracks. This paper focused on the qualitative and quantitative analysis of CT scanning images of the height of a 7/16 cross section at the different strain for three kinds of soil samples. Using the program self-prepared in Matlab software, the CT scan images were binarized, and the statistical crack data of the scan layer section were obtained including the crack rate of cross section, the total crack size in the area near the root and beyond the root respectively, and the length and width of the maximum crack area. Through the comparative analysis of CT scan images evolution under pressure and the statistical crack data of them for the non-rooted soils and the rooted soils, the fundamental differences in destruction process of the soil and crack propagation between the non-rooted soil and the rooted soil were described, thus exposing the crack resistance and the bridging effect of roots. It was concluded that the mesomechanics mechanism of roots reinforcement is mainly the crack resistance and the bridging effect of root on the soil. [ABSTRACT FROM AUTHOR]