The invention relates to a preparation method of a high-strength fluorine-containing polymer. The method comprises the following steps: 1) adding water and an emulsifier to a reactor, and evacuating until the oxygen content is smaller than or equal to 50ppm; 2) continuing to add a pH regulator and a chain transfer agent; 3) heating the reactor to 40-60 DEG C, and adding a mixed monomer composed of 1,1-difluoroethylene, tetrafluoroethylene and trifluorochloroethylene; 4) adding an initiator, beginning polymerization reaction, and lastingly adding the mixed monomer to maintain the pressure inside the reactor constant in the polymerization reaction; and 5) finishing the polymerization reaction when the solid content of a polymer emulsion achieves 25-35% by mass, freezing and condensing the emulsion, washing and drying, so as to obtain the fluorine-containing polymer which is relatively high in strength, good in ageing resistance, and good in mechanical property and has the molecular weight of 150,000-300,000. The preparation method of the fluorine-containing polymer, which is disclosed by the invention, is fewer in raw materials, simple in technology, and applicable to large-scale popularization.