The invention belongs to the field of sliding nozzle, and more specifically relates to a sliding plate waste material powder, a preparation method thereof, a sliding plate external layer material, anda sliding plate. The preparation method comprises following steps: waste sliding plate mud and collected dust generated in sliding plate treatment process are subjected to aging treatment so as to obtain a pug, and the pug is dried until water content is reduced to be 15% or lower; carbon sealing treatment is carried out, and powder grinding is carried out until particle size ranges from 150 to 200 meshes; and iron is removed so as to obtain the sliding plate waste material powder. According to the preparation method, direct utilization of waste materials is realized, storage space is reducedgreatly, production benefit is excellent, production cost is reduced, and the environment is protected. The obtained sliding plate waste material powder can be used in sliding nozzle external layer materials, the qualified rate and the utilization effect are stable; the qualified rate is equal to that of products containing no waste sliding plate mud and collected dust, and is as high as 95%; theutilization effects in steel mills are the same, the continuous sliding rate is 1.8 times; the cost of each ton of raw materials is reduced by 300 to 400yuan.