The invention belongs to the field of polysiloxane microemulsion, and discloses an electrolyte-resistant and high-solid content polysiloxane microemulsion, and a preparation method and application thereof. The preparation method comprises the following steps of dissolving a composite surfactant in water, adding a part of organic siloxane monomers, and performing shearing emulsification and high-pressure homogenization to obtain siloxane monomer pre-emulsion; adding electrolyte, performing heating and stirring, and adding a catalyst for thermostatic reaction; adding dropwise the residual siloxane monomers, continuing reaction, cooling a reaction product to room temperature, and neutralizing the reaction product to be neutral to obtain the polysiloxane microemulsion. According to the polysiloxane microemulsion, and the preparation method and application thereof, the compound surfactant is used, so that the using amount of an emulsifier is reduced, the stability of an emulsion system is improved, the conversion rate of the emulsion system is increased, and the solid content is increased; the polysiloxane microemulsion has the characteristics of high hydrophobicity, low-temperature resistance, high-temperature resistance, water resistance, electrolyte resistance and alkali resistance, is free of a metal catalyst, and can be widely applied to the fields of textile, leather, cosmetics, medicines, buildings and the like.