Preparing method for producing flame-retardant polyester fibers through recycled polyester bottle flakes

The invention relates to a preparing method for producing flame-retardant polyester fibers through recycled polyester bottle flakes. The preparing method includes the step of preparing flame-retardant polyester parent materials, wherein 28 mass parts to 32 mass parts of ethanediol, 68 mass parts to 72 mass parts of purified terephthalic acid, 80 ppm to 300 ppm of antimony-based catalysts and 100 ppm to 500 ppm of stabilizers are added into a pulping kettle to be stirred and prepared into pulp I; the pulp I is guided into an esterification kettle and heated to 245 DEG C to 260 DEG C to be esterified, 15,000 ppm to 30,000 ppm of flame retardant assistants, 0 mass part to 1.2 mass parts of flatting agents and 200 ppm to 500 ppm of antioxidants are added for continuously carrying out the esterification reaction, and flame-retardant bis(2-hydroxyethyl)terephthalate II is prepared; the flame-retardant bis(2-hydroxyethyl)terephthalate II is guided into a condensation polymerization kettle to be heated, the vacuum degree is controlled to be 1,200 Pa to 1,800 Pa, and pre-condensation polymerization is carried out; then the vacuum degree is adjusted to be lower than 80 Pa, and heating is carried out for condensation polymerization till the condensation polymerization reaction is finished; the flame-retardant polyester parent materials III are obtained through band casting, cooling and pellet cutting, and the content A ppm of P of the flame-retardant polyester parent materials III is detected.