Abstract: Mechanical shearing systems are commonly used in reprocessing plants to crack spent fuel. The radioactive dust generated by shearing needs to be contained to ensure the full utilization of spent fuel pellets and the maintainability of the hot chamber. The airflow pattern and particle distribution and movement in the machine are of great significance to ensure the normal operation of the shearing machine. In order to supplement the deficiencies of experimental research and theoretical research, and improve dust distribution, reduce dust levels and optimize design of the shearing machine, the flow field in bar shearing machine with injected virtual particles was simulated based on the discrete particle model. By analyzing the distribution of velocity, pressure and turbulent kinetic energy of the fluid in shearing machine and the destructive effect of dust particles on the inner wall of shearing machine, the structure and boundary conditions of the shear were optimized. The results show that the eddy current, turbulence and high impact force can be effectively avoided by improving the structure of the flow passage and the input conditions. The velocity field, pressure field and turbulent kinetic energy distribution of gas-solid two-phase flow in the box are more uniform and the gradient change is smaller, and the damage of box wall is effectively reduced.