Abstract: The hydrotalcite-PU flame retardant agent was prepared by compositing hydrotalcite into waterborne PU, then applied on the polyester fabrics. The mechanism of flame retardant and moisture permeability were studied through the hydrotalcite structures, which characterized by X-ray diffraction (XRD) and infrared spectroscopy (FT-IR); and the performance of the coated fabric, which tested by thermogravimetry (TG) and scanning electron microscope (SEM)) and so on. The results show that the combustion of coated fabric is retarded because the hydrotalcite plays a multi-role of an endothermic and cooling process, then gas phase diluted, at last forming heat insulation layer on the fabric surface during the burning process. And the moisture permeability is improved because the hydrophilic group in hydrotalcite.