The present invention relates to a method for preparing a phase-separated lead telluride-lead sulfide nanopowder using solution synthesis and a phase-separated lead telluride-lead sulfide nanopowder prepared by the method. The method includes: (a) mixing tellurium and a first solvent, followed by ultrasonic irradiation to prepare a tellurium precursor solution; (b) mixing an organosulfur compound and a second solvent, followed by ultrasonic irradiation to prepare a sulfur precursor solution; (c) mixing lead oxide, a third solvent, and a fourth solvent and heating the mixture to prepare a lead precursor solution; (d) adding the tellurium precursor solution to the lead precursor solution and allowing the mixture to react; (e) adding the sulfur precursor solution to the reaction mixture of step (d) and allowing the resulting mixture to react; and (f) cooling the reaction mixture of step (e) to room temperature to prepare a phase-separated lead telluride-lead sulfide nanopowder.