The invention discloses a solid scale inhibitor and a preparation method thereof. The solid scale inhibitor comprises a main scale inhibitor and a cementing agent, the proportion of the main scale inhibitor to the cementing agent is 1:1, wherein the main scale inhibitor comprises, by weight, 35-50 parts of 1-Hydroxyethylidene-1,1-diphosphonic acid, 30-45 parts of polyhydric alcohol phosphate ester, 1-5 parts of sodium hexametaphosphate and 5-10 parts of sodium molybdate; the cementing agent comprises, by weight, 3-5 parts of alum, 20-30 parts of epoxy resin, 7-10 parts of polyamide, 13-15 parts of epoxy diluent and 17-20 parts of silane coupling agenta. Thus, after the solid scale inhibitor is in use, the cycle of agent efficacy release is long, the antiscale rate is high, the scaling on devices, pipelines and the like can be prevented in the petroleum processing process, the number of times of filling is reduced, and therefore a continuous production cycle of petroleum processing devices is increased, the manpower and financial resource input is reduced, and the production cost is reduced.