The invention relates to a method for preparing retardant resorcin phosphate. The method comprises the following steps: heating phosphorus oxychloride, catalyst and water absorbent until the phosphorus oxychloride flows back; cooling the mixed solvent to a temperature between 80 and 85 DEG C, and adding melted resorcin liquid to the mixed solvent; heating the mixed solvent to a temperature between 110 and 115 DEG C to react so as to obtain an intermediate product, wherein dosage of the catalyst is 1 to 2 percent of the resorcin by weight, dosage of the water absorbent is 0.1 to 0.5 percent ofthe resorcin by weight, and the molar ratio of the phosphorus oxychloride to the resorcin is 3.5-4.5:1; adding the catalyst and the water absorbent into the intermediate product, heating the mixture to a temperature between 120 and 125 DEG C; adding melted phenol liquid to the mixture to obtain a product, wherein dosage of the catalyst is 2 to 4 percent of the resorcin, dosage of the water absorbent is 0.1 to 0.5 percent of the resorcin by weight, and molar ratio of the phenol and the resorcin is 3.75-3.80:1. The content of the resorcin phosphate is more than or equal to 99 percent, content of triphenyl phosphate is less than or equal to 1 percent, so the retardant resorcin phosphate has excellent thermal stability, volatility, migration and durability.