The invention provides a preparation method of fluorine-containing polymer concentrated dispersion liquid. The method comprises the following steps: heating an aqueous polymerization solution of a fluorine-containing polymer to 60-90 DEG C, adding an emulsifying agent which accounts for 2-10% of the dry material quantity of the polymerization solution and 0.03-0.8% of inert salt in percentage by weight into the aqueous polymerization solution, and stirring to obtain an emulsion; heating the emulsion to 75-118 DEG C, standing for 2-5 hours at 75-118 DEG C, layering the emulsion, and separating out the lower-layer emulsion namely the fluorine-containing polymer concentrated dispersion liquid. By adopting the method provided by the invention, a fluorine-containing polymer concentrated dispersion liquid product which is good in appearance and good in stability can be prepared. The product stability is generally more than 300 seconds. The preparation method of the fluorine-containing polymer concentrated dispersion liquid, provided by the invention, is simple in process, strong in operability, high in concentration efficiency and low in energy consumption, and is suitable for industrial production.