The utility model discloses a cable sealing device for an underwater platform, which comprises a sealing shell of a cylindrical structure. The two ends of the sealing shell are respectively and threadedly connected with a compaction end cover. The inner sides of the two compaction end covers are respectively and sequentially provided with a spring energy storage assembly, a trapezoidal upper gasket, a rubber sealing gasket, and a trapezoidal lower gasket. Each rubber sealing gasket is of a ring-shaped structure with a trapezoidal groove. Both the trapezoidal upper gasket and the trapezoidal lower gasket are of a ring-shaped structure with a trapezoidal projection. The spring energy storage assembly is composed of two butterfly-shaped spring gaskets and the two butterfly-shaped spring gaskets are combined oppositely to form the spring energy storage assembly. During the application process of the cable sealing device for the underwater platform, the compaction end covers, the spring energy storage assembly, the trapezoidal upper gasket, the rubber sealing gasket and the trapezoidal lower gasket are respectively and orderly sleeved onto one end of a cabin-crossing cable and an equipment cable. After that, the cabin-crossing cable and the equipment cable are respectively put into the sealing shell to be connected together and tightly compacted inside the hydraulically sealing shell by means of the compaction end covers. Therefore, the cable connection of the underwater platform with external equipment is ensured to be reliable and sealed.