Abstract: In view of the frequent failure of the reducer of the slag roller grinding machine, special protective measures were made. When the vibration value of the mill exceeded 15mm/s, after the delay of 5s the mill would stop; a horizontal and vertical vibration sensors was installed at the high-speed shaft of the reducer. When one of the vibration values exceeded 4mm/s, after the delay of 4s the mill would stop. The material feeding should be uniformed, and the specific gravity of the particle size of less than 20mm should be controlled more than 95%. The advanced point inspection instrument was used to strengthen the point inspection and the data was automatically analyzed. Other operations were suggested, such as check the inside of the reducer regularly, check the filter of the reducer oil station regularly, choose suitable lubricating oil products, monthly analyze the deceleration engine lubricant, replace the lubricant according to the inspection results.