Abstract: A coupling simulation method and experiment based on DEM−CFD were investigated to address the complex multi−phase coupling motion of spiral agitators, grinding media, and slurry inside the cylinder of a vertical stirring mill. Firstly, based on the working principle, the Discrete Element Method (DEM) was used to simulate the particle phase and Computational Fluid Dynamics (CFD) to simulate the fluid phase, respectively. A theoretical model of fluid−solid coupling inside the cylinder was constructed. Secondly, a simplified model of the experimental prototype was established, and the construction methods and parameters of the grinding sphere (DEM), slurry (CFD), and DEM−CFD coupling model were investigated, respectively. Then, the accuracy of different simulation models was verified by experiments. The results showed that the DEM−CFD simulation results were closer to the experimental values than DEM, there was a deviation of 5.43% between the torque obtained from DEM−CFD model and the experimental torque, while the DEM model had a deviation of 8.14%. By comparing the velocity, collision frequency, and agitator torque of the grinding spheres inside the cylinder, it was found that the slurry as a fluid domain had a significant impact on the movement of the grinding spheres. Its buoyancy and viscosity characteristics reduced the velocity and collision frequency, whereas it increased the torque of the spiral agitator.