The invention discloses a production method of Lycra polyester composite filaments. The production process includes the steps of original filament erecting, press rolling, roller arrangement, disc heating, plate heating, disc cooling, spooling nozzle arrangement, grooved drum arrangement, winding, appearance inspection, physical index detection, finished product grading, encasement and packaging. A pre-drafting mode is adopted to POY, the pre-oriented yarn is properly stretched through the stretch ratio of 1.0-1.1, FDY is introduced into a grid-connected system, the FDY and the POY which is being pre-drafted are subjected to mixed drafting, the stretching temperature of 98-98 DEG C is used in the pre-drafting process, the shaping temperature of 135-142 DEG C is used in the mixed drafting process, and the grid-connection air pressure of 3.5-3.9 kg is used in the grid connection process. According to the production method of Lycra polyester composite filaments, a conventional drafting grid connection machine can be used for producing polyester composite filaments which is deeply and evenly dyed and good in elasticity, the polymer composite filaments and cotton yarn are blended during later processing, spandex (Lycra) fiber is added in the weaving process, and the composite filaments can become an ideal raw material of high-grade thin woolen sweaters for females.