The invention relates to the technical field of polyester filaments, in particular to a preparing method for a colorful polyester filament. A polyester melt is treated through a metering pump, a spinning assembly, a spinning box, a pigment dyeing mechanism, an oiling groove, a stretching shaping mechanism and a winding forming mechanism; the pigment dyeing mechanism is arranged on the polyester filament delivered between the spinning box and the oiling groove, pigment is evenly sprayed to the circumferential-direction surface of the polyester filament through the pigment dyeing mechanism, thepigment dyeing mechanism is located above the oiling groove, the distance between a pigment spraying nozzle of the pigment dyeing mechanism and the oiling groove is 0.1 m to 0.6 m, and the concentration of an oiling agent for oiling in the oiling groove is 6% to 10%. According to the production method of the colorful polyester filament, simplification of production of the colorful polyester filament is achieved, small-batch fast producing and process is achieved, and trial production and the like of the polyester filament is greatly convenient.