The computational cost of the Discrete Element Method (DEM) increases sharply with the number of particles. Improving the computational speed of DEM for industrial-scale particle flow problems has long been a critical bottleneck to be addressed in this field. Based on the principle of consistent energy dissipation rate between the scaled and original systems, this paper proposes a coarse-grained discrete element method suitable for shear particle flows. It replaces a large number of original small particles with a small number of enlarged coarse particles to improve computational efficiency. Numerical simulations were conducted using the particle mixing process in a rotating drum as a case study. The results show that the deviations in mixing characteristics, velocity distribution, and total kinetic energy between the coarse-grained system and the original system in the rotating drum are 6.2%, while the computational time is reduced by 188 times. The proposed coarse-grained DEM can significantly improve computational efficiency while ensuring accuracy, effectively solving the problem of efficient and precise simulation of industrial-scale particle flows.