The invention belongs to the technical field of preparation of polysiloxane emulsion, and discloses a method for synthesizing polysiloxane miniemulsion by utilizing microlatex seeds under a single emulgator as well as the polysiloxane miniemulsion and application of the polysiloxane miniemulsion. The method comprises the following specific steps of dissolving the emulgator in water, adding an organosilicone monomer, mixing mechanically for pre-emulsification, adding a super basic catalyst after heating, and mixing at a constant temperature to obtain the organic siloxane microlatex seed emulsion; dropwise adding the organosilicone monomer in the organic siloxane microlatex seed emulsion semi-intermittently while mixing at the constant temperature, mixing continuously at the constant temperature for reaction after the dropwise adding, cooling, and neutralizing to obtain the polysiloxane miniemulsion. According to the method, long-chain alkyl-di-polyoxyethylene quaternary ammonium salt is used as the single cationic emulsifier, the polysiloxane microlatex is used as seeds, the same monomer is added semi-intermittently, the polysiloxane miniemulsion which is small in grain size, narrow in distribution and good in stability is prepared without relying on other homogenizing means, and the polysiloxane miniemulsion can be widely applied to the fields of textiles, coatings and household chemicals.