The present invention is directed to a method for preparing a polyester fiber, the method including: mixing 5-50 wt % of composite metal oxide particles, including a tungsten-based oxide, a cesium-based oxide, an antimony-based oxide, an indium-based oxide, and a tin-based oxide, with 40-90 wt % of one or two types of organic solvents selected from among alcohol, ketone, and acetates, 0.4-20 wt % of polyvinyl butyral, i.e., polymer, and 2-30 wt % of calcium stearate or magnesium stearate to obtain a mixture, and stirring and grinding the mixture to prepare a dispersion liquid; drying the dispersion liquid to prepare a powdered additive; mixing 1-30 wt % of the additive with polyester chips to obtain a mixture and melting this mixture to prepare master batch chips; and mixing 1-10 wt % of the master batch chips with general polyester chips to obtain a mixture, and melting and spinning this mixture.