The invention provides a method for preparing high-concentration coal water slurry through a rod mill. The method comprises the following steps that 1, coal, water and an additive are mixed into a coal-water mixture; 2, the coal-water mixture is added into the rod mill to be grinded so as to obtain crude coal water slurry; 3, purities in the crude coal water slurry are removed through a drum screen to obtain fine coal water slurry, and the fine coal water slurry is transported into a coal water slurry storage tank for standby. The coal water slurry in the rod mill is grinded three times, grinding media in the rod mill are steel rods, and the steel rods comprise three steel rods of different diameters. The coal water slurry prepared by the method has the advantages that the viscosity is moderate, the size distribution of coal slurry is uniform, no stratification occurs, effective gas components of crude gas of an outlet of a gasification furnace can be increased to 81% or above when thecoal water slurry is in use, the coal consumption for each ton of ammonia is reduced, the yield of synthetic ammonia is increased, and the production cost is reduced.