The invention discloses an epoxy group containing polysilsesquioxane sulfonate, and a preparation method and applications thereof. The preparation method comprises following steps: a, a mercapto trialkoxysilane monomer is added into an aqueous solution containing an anionic surfactant and an alkali catalyst for reaction; b, after reaction in step a, with stirring, under ultraviolet lamp illumination, p-styrene sulfonate, glycidyl methacrylate, and 1-hydroxycyclohexyl phenyl ketone are added successively; c, after reaction in step b, solid liquid separation is carried out so as to obtain a solid product; and d, the solid product obtained in step c is subjected to washing and drying so as to obtain a finished product. According to the preparation method, grafting of the sulfonate and the epoxy groups onto the polysilsesquioxane chains of the epoxy group containing polysilsesquioxane sulfonate is adopted, so that the compatibility with PC is excellent, dispersion is convenient, migrationresistance is achieved, pollution is less, and an extremely low adding amount is capable of improving PC flame resistance grade to be UL94V-0 grade (1.6mm), and the durability is excellent.