In view of the shortage of analysis studies on the influence factors of the degradation of gradation of grain and influence law of the transport parameters for the coal particle degradation during the coal slurry conveying, a test method is used to study the influences of the coal slurry velocities, particle size and pump conveying time on the particle size distribution degradation during the coal slurry conveying. At the same time, the analysis of influences of the coal slurry gradation degradation on the slurry viscosity, pipeline transportation resistance and siltation velocities is also carried out through the experimental method and theoretical analysis method. From the test analysis results it is found that the higher the flow velocity of the slurry is, the longer the pumping time is, and the larger the particle size is, the greater the degradation rate of the particles is. The results of experimental survey and theoretical analysis show that the slurry viscosity has increased, the resistance has decreased, and the non-silting velocities relevantly decreased due to the degradation of the coal slurry gradation. And the viscosity and resistance values can be accurately estimated by the Fei Xiang-jun viscosity and resistance model. On the basis of the research results mentioned above, a calculation model for the critical silting velocities is developed in this paper.