The invention provides a preparing method for polyester fabric for leggings. By blending polyester fibers, kapok fibers and polyamide fabric, very good thermal insulation and antibacterial effects can be achieved, and meanwhile very good drapability and body shaping performance are achieved; environment-friendly treatment is carried out on kapok fibers, and thus kapok fibers are made to have good thermal insulation performance; no chemical preparation is used except food-grade glycerin, and the novel fiber preparing method is environmentally friendly.