The invention provides a system and method for preparing pulverized coal fuel of a pulverized-coal boiler by using coal washing tailings. The system includes a slurry mixing device, an impurity removing and coarse-grain material intercepting device, a grading recovery device, an ore pulp pretreatment device, a coal slime separating device, a coal slime water purifying device, a concentrate dehydration device and a thermal power drying device which are connected in a scientific mode. The method for preparing the pulverized coal fuel of the pulverized-coal boiler through the system comprises the steps of mixing ore pulp, removing impurities in the ore pulp, intercepting coarse-grain materials in the ore pulp, feeding the ore pulp into the grading recovery device for grading, adding floatation agents for pretreatment, feeding the ore pulp into a fine-grain coal slime separating device for separation, dehydrating and drying selected concentrate, feeding the tailings into a coal slime water treatment device for solid-liquid separation, and recycling purified tailing water. By means of the system and method for preparing the pulverized coal fuel of the pulverized-coal boiler by using the coal washing tailings, the pulverized coal fuel meeting the combustion requirements of the pulverized-coal fluidized bed boiler is prepared without the grinding step, emission of the coal washing tailings is reduced, the environment is protected, comprehensive utilization of resources is realized, resources are saved, and the utilization efficiency of coal resources is improved.