The backfilling materials of high concentration cemented material backfilling mining technique consist of coal waste rocks, coal ash, cement, additives and water. After mixing to become a high-density mixture it is pumped through pipelines to underground and then move to fill the gob. The backfilling method can both depose the coal waste rocks and extract the coal resources under the villages. Before and after pumping the high concentration cemented material, the coal ash slurry must be pumped first. So the coal ash slurry characteristics directly affect the filling effect. With the help of the particle-size analyzer to analyze the characteristics of the coal ash, the range of particle size distribution has been obtained for four kinds of coal ash. On the basis of analyzing the data obtained by laboratory rheological experiment, the rheological model for the coal ash slurry is determined. Based on theoretical analysis, the frictional and local resistance losses of the coal ash slurry through pipeline transportation are analyzed.