The invention discloses a high-strength compound cable sealing sheath for underwater detection. The high-strength compound cable sealing sheath is prepared through controlling technological steps and raw materials of the high-strength compound cable sealing sheath for the underwater detection by utilizing a technology of carrying out two times of internal mixing, one time of open mixing, one time of extrusion and microwave vulcanization. The compound cable sealing sheath disclosed by the invention is prepared by carrying out two times of the internal mixing, one time of the open mixing, one time of the extrusion and the microwave vulcanization on the raw materials; especially, under the condition that the temperature of the second-time internal mixing is 22 DEG C to 37 DEG C higher than the temperature of the first-time internal mixing, the strength and the corrosion resistance of the prepared cable sealing sheath are remarkably improved. Moreover, a preparation method of the cable sealing sheath is simple and easy to popularize and has relatively high application value.