Abstract: Abstract: This article aims at improving the efficiency of straw the rubbing machine 9R-40 by by optimizating of its hammer. The working mechanism of rubbing machine was describled in detail from the aspects of the feeding performance, impact damaging, rubbing, and transport of straw. Analysis shows that variation of the equivalent thickness of the hammer can affect the collision probability and the impact pressure. Furthermore, changes on angle of the hammer, which is related to the cross section of the spindle, can adjust the structure of the inner flow field. Therefore, this paper presents a new method to improve the efficiency of this machine by using variable angle hammer. Tilt hammer changes the angle between the top blade of the hammer and the moving plane, while maintaining the same shape and size of the original hammer. CFD method was used to compare the variation of internal flow field excit at by no inclination angle hammer and 8 degree angle (estimated by the theoretical analysis) hammer, based on the single-phase numerical simulation of flow field in rubbing machine taking the inclination angle as the structure parameter of the hammer. In this paper, the Z-axis represents the principal axis of the 3D modeling of the rubbing machine. Value of Z varied in the range of 0-700mm, the number of Z is larger, which means it is closer to the import of the machine. The author selected representing feeding section 700, 600, 500mm, and selected representing rubbing section 700, 600, 500mm. Simulation results shows that the dynamic pressure in the flow field of rubbing machine caused by tilt hammer varies between 4.13e-2, 5.43e3. The flow field of common hammer is between 3.62e-2, 5.2e3. The dynamic pressure is larger, the static pressure is smaller in the case of the same total pressure, which means that the airflow caused by tilt hammer can overcome the resistance of inner wall of rubbing machine. In addition, maximum velocity of internal flow field caused by tilt hammer is 94.1m/s, which is more than 91.8m/s caused by common hammer. It means that tilt hammer can produce larger air drag force, so as to enhance the equipment efficiency effectively. These results show that the tilt hammer is more favorable to the flow field structure, which is beneficial to the material processing and transportation compared with the common hammer. At last, the simulation results of the internal flow field verifies the results of theoretical analysis and numerical calculation, which testify hammer can achieve high energy rubbing by regulating the flow field. This study enriches the theory of the category of hammer，put forward a new structure parameters which is hammer angle and its design principle. This research provides a new perspective for parameter optimization of hammer of rubbing machine, and offers a theoretical basis for optimization of energy conservation of this kind of Livestock machine as well.