The traditional coal mill liner will unavoidably wear and deform over time. It causes significant changes in the movement law of the grinding medium in the cavity and significantly lowers the efficiency of coal breaking. In this study, the ?4.04 × 5.54 m coal mill in a thermal power plant was taken for research, and the evolution process of the grinding medium movement before and after the wear of different cavity liners was explored. The flow state of the grinding medium, the collision relationship, the coal breaking efficiency, and the impact energy of the liner were modified and optimized. At the same time, the method of adjusting the mill barrel speed to promote the efficient coal breaking of the worn liner was used. The research investigates the variation in barrel speed effect on the law of medium flow. The results show that the coal breaking efficiency of the improved liner cavity is increased by 21.7 %, and the service life of the liner is prolonged. It is feasible to increase the cylinder speed to compensate the low coal breaking rate caused by the wear of the liner. The maximum coal breaking rate could be increased by 98.6%. And the normal and tangential cumulative contact energy of the liner might be increased by 144.9% and 54.9%, respectively, which accelerates the consumption of worn liners. The study provides theoretical guidance for improving coal utilization and production efficiency.