Objective To solve the problems of particle crushing and overgrinding of rice in horizontal milling machines, it is proposed to improve the milling quality of brown rice particles by changing the direction of suction air flow.Methods The CFD-DEM coupling method is used for the numerical simulation of the three states of upward suction at 10 m/s, downward suction at 5 m/s, and no wind speed (0 m/s). The simulation results are verified by the milling test with the physical prototype.Results As the air flow direction changes from upward suction to downward suction, the ascending velocity v_y and triaxial synthetic average velocity v of rice particles along the Y axis show an overall decreasing trend, and the upward suction particle velocity v_y is greater than the downward suction particle velocity v_y at the same layer. It is observed that the average velocity v of upward suction particles is larger than that of downward suction particles in the middle and lower parts of the whitening chamber. The difference in the movement capacity of the particles in the grinding area leads to a significant difference in the force in the areas prone to overgrinding and crushing. When the particle movement capacity is strong, the extrusion pressure on the particles at the bottom of the whitening chamber decreases. When the particle movement capacity is weak, the extrusion pressure on the particles at the bottom of the whitening chamber increases. In the case of upward suction, the rolling angular velocity of particles is higher than those in the cases of no wind speed and downward suction. According to the results of three physical tests in each state, the average degree of milling (D_OM) under upward suction at 10 m/s, no wind speed, and downward suction at 5 m/s are 1.90%, 2.20%, and 2.78%, respectively, and the average rate of crushing (R_OC) are 0.37%, 0.46%, and 0.60%, respectively.Conclusion The flow and force characteristics of the particle milling process under upward suction are superior to those under no wind speed and downward suction. The D_OM and R_OC under upward suction are significantly lower than those under no wind speed and downward suction.