A preparing method of a tetrafluoroethylene-hexafluoropropylene copolymer concentrated dispersion liquid is provided. The method includes: adding polyoxyethylene aliphatate and a metal chelating agent into an aqueous polymerization solution of tetrafluoroethylene-hexafluoropropylene copolymer, mixing uniformly, heating, concentrating under vacuum until the solid content is 30-70 wt%, and adding a pH conditioning agent into the concentrated dispersion liquid to adjust the pH value of the dispersion liquid to 5-10, then a finished product of the tetrafluoroethylene-hexafluoropropylene copolymer concentrated dispersion liquid is obtained. The product is free of floating substances and color changes after the product is allowed to stand for 6 months. The stability of the product can be higher than 300 s. The method has characteristics of simple process, high operability and high concentration efficiency, and is environmental friendly and suitable for industrial production.