The invention discloses a preparation method of fluorine-containing microemulsion which is prepared from hexafluoropropylene, tetrafluoroethylene and trifluoropropene under the action of assistants of an initiating agent, an emulsifying agent and the like through combined polymerization, wherein the fluorine-containing microemulsion comprises the following copolymers in percent by mass: 40-70 percent of hexafluoropropylene, 30-60 percent of tetrafluoroethylene and 1-20 percent of trifluoropropene. The fluorine-containing microemulsion prepared in the invention has low surface energy, plays a role of preventing water, oil and dirt when being coated on the surface of an object, and can be used as a coating agent, a fabric finishing agent and a coating.