The invention discloses a method for preparing a flame-retardant eight-hole brick by using paper mill sludge. By utilizing the paper mill sludge, the pollution is reduced; meanwhile, the toughness andstrength of the eight-hole brick are improved; glass beads are added, so that the flame-retardant effect is improved; by adopting lime water to pretreat the paper mill sludge first, the corrosion resistance of the eight-hole brick can be improved. The product has the advantages of wide range of raw materials and simple production process; the quality and performance of the product are significantly improved as compared with a traditional eight-hole brick.