The development pattern and distribution characteristics of the shear zone of the particle direct shear test determine the strength of the particle body, but it is not easy to observe. The direct shear test of transparent polycarbonate particles was carried out using a homemade test device. Based on the principle of photoelastic method, the development process of force chain, the development law of main contact angle and the development law of shear slip surface of particles were studied by observing the shear mechanical properties, stress chain distribution and displacement field of particles, and the simulation analysis was carried out in PFC2D discrete element software. The tests show that: the stress shielding phenomenon exists in the force chain distribution of the particle system during the direct shear process; the strong force chain, contact angle and main stress direction of the particle system are deflected, and the deflection characteristics are basically the same; the particles form an arch-shaped shear slip surface during the shear process, and form an arch-shaped slip shear zone together with the horizontal shear surface. The arch slip zone forms at the beginning of shear and continues throughout the shear process. At peak shear stress, the height of the arch-slip zone is proportional to the initial normal force and is between (13~15) d50 thick. The arch slip zone gradually decreases during the residual stress phase, and the arch slip zone gradually tends to a steady state, and the height of the arch slip zone under different initial normal forces does not differ significantly during the residual stress phase,and thickness between (8~9) d50.