Taking the grinding system of "CLF170-100 roller press + ?4.2m×12.5m ball mill" in the 5 000t/d cement production line as the research object.  The relationship between the gradation of the grinding media in the ball mill and the particle size of the material entering the mill was analyzed, as well as the problem of the excessively wide particle size of the material entering the mill. By transforming the structure of the side baffle of the roller press, adding two dispersing devices in the feeding chute above the V-type separator, and adding a zipper conveyor below the discharger of the dust collector in the roller press system, and optimizing the fineness of the returned ash of the dust collector in the pre-grinding system, the over-grinding of the ball mill has been effectively solved. After the transformation, the ball mill operates stably, the quality of the finished cement is significantly improved, the hourly output is increased by 10t/h, the comprehensive power consumption is reduced by 1kW·h/t, and the electricity cost can be saved by about 36 000 yuan per month, with remarkable social and economic benefits.