The invention discloses a phosphogypsum wall brick, which comprises the following raw materials in parts by weight: 90-105 parts of phosphogypsum, 6-10 parts of carbide slag, 8-15 parts of hydraulic admixture, 5-8 parts of rough stone, 10-16 parts of stone powder, 0.5-2 parts of anhydrous sodium sulfate, 3-5 parts of water glass, 0.05-0.2 part of calcium formate, and 2-6 parts of calcium lignosulphonate. The wall brick has the characteristics of light weight, high strength, low water absorption, high softening coefficient and good freezing resistance, is suitable for a building load-bearing and spacing wall body. The invention also discloses a preparation method of the phosphogypsum wall brick. According to the method disclosed by the invention, large quantities of industrial waste residue phosphogypsum is effectively utilized, the building material resource comprehensive utilization of the phosphogypsum can be achieved; meanwhile, a phosphogypsum and carbide slag composite pelletizing technology is adopted harmful substances in the phosphogypsum raw material can be removed, and the softening coefficient and strength of a phosphogypsum product can be increased.