A flame-retardant polyester artificial hair filaments is provided which comprises: (A) 100 parts by weight of a thermoplastic polyester resin; (B) 10-30 parts by weight of a polymeric phosphorus-based flame retardant; (C) 0.1-3 parts by weight of a chain extender; and (D) 0.5-3 parts by weight of sodium antimonate. The polymeric phosphorus-based flame retardant (B) may be a flame retardant having a repeat unit of formula 1 and a weight-average molecular weight ranging from 80,000 to 150,000. The flame-retardant polyester artificial hair filaments can be prepared by: extruding a composition comprising a mixture of a polyester resin, a polymeric phosphorus-based flame retardant, a chain extender and sodium antimonate to form a pellet; drying the pellet to a water content of 500 ppm or less; melt-spinning the dried pellet to prepare a undrawn yarn; drawing the undrawn yarn at a draw ratio of 2-5; and heat-treating the drawn yarn in a heat treatment device heated to a temperature of 150˜280° C.