Abstract: The fragmentation and naturalness of soils make their deformation and strength characteristics have obvious scale effects. Therefore, in order to study the strain localization process of the soils, the distribution and proportional relationship of graded particles cannot be ignored, and the macroscopic mechanical properties must be characterized from multiple scales. Based on the theory of cell model, the soils are regarded as a granular material composed of reinforced particles and matrix. The intrinsic scale law of the samples with different reinforced particle sizes is studied through the triaxial compression tests, and the formation process and initiation mechanism of shear band at meso level are studied through the numerical simulation. The average strain energy release coefficient is introduced to quantitatively verify the strain energy conversion of the soils after reaching the peak stress, and the multi-band initiation and progressive competition process are reproduced. The results show that the strength tests of reinforced particles with different size scales indicate that the discontinuity of particles makes the soils have size effects, and the ratio of intrinsic scale to particle size decreases with the increase of the reinforced particle size. Before the stress peak, the non-elastic dissipative energy increases, leading to strain localization. After the peak, the strain rapidly increases within the shear band, while there is a rebound outside the band.