Abstract: In view of the lack of research on the prediction of particle gradation degradation in the transportation of coarse particle coal slurry, by using the experimental research method and theoretical analysis method, the mass percentage, viscosity and hydraulic gradient of each particle size in coal slurry at 30, 40, 50 and 60 min are given out. The idea of using grinding theory to study the coal conveying process of coarse coal slurry pipeline is put forward. On this basis, the solution methods of breakage rate function and grinding balance equation are given. The results of data comparison and analysis show that the maximum deviation between the predicted value and the measured value of particle gradation is no more than 12.53% when the coal slurry is transported for 30 and 50 min. With the extension of conveying time of coarse coal slurry, the relative viscosity of coal slurry gradually increases, mainly due to the refinement of coarse particles above 2.0 mm and the increase of particle content below 0.074 mm. The reduction of hydraulic gradient caused by particle grading degradation is mainly due to the reduction of settlement velocity caused by coarse particle refinement and the reduction of the probability of particle contact with the bottom of the pipeline.