The invention discloses a PMA-EVA high-strength cable sealing sheath and a preparation method thereof. The preparation method comprises the steps that (1), sodium silicate and a sulfuric acid solution are mixed to form hydrogel; (2) bentonite is soaked in a hydrochloric acid solution for activating treatment, and then filtration is performed to get a filter cake so as to prepare a modifier; (3) PMA (polymethyl acrylate), EVA (ethylene-vinyl acetate copolymer), a complex shown in the formula (I), talcum powder, ethyl formate, hydrazine, arbutin, diborane, pentaerythritol, triallyl cyanurate, 2-benzothiazolethiol, the hydrogel and the modifier are mixed, cooled and shaped to prepare the PMA-EVA high-strength cable sealing sheath. The PMA-EVA high-strength cable sealing sheath prepared through the method has excellent mechanical properties, corrosion resistance and pressure resistance.