The invention discloses a core pressure-maintaining coring drill tool for a submarine natural gas hydrate and belongs to the technical field of well drilling equipment. The core pressure-maintaining coring drill tool is matched with a rope fishing coring-drilling technique and comprises an inner pipe assembly and an outer pipe assembly. The outer pipe assembly is of the structure of a vertically-through cavity, the upper end of the outer pipe assembly is connected with a drill rod, and a drill bit is arranged at the lower end of the outer pipe assembly. The inner pipe assembly is placed in the cavity of the outer pipe assembly. A core pipe is arranged at the lower end of the inner pipe assembly, and a clamp spring and a clamp spring seat are arranged at the lower end of the core pipe. The core pressure-maintaining coring drill tool is characterized by further comprising a pressure compensation system; the pressure compensation system is provided with a pressure-maintaining cap assembly; the pressure-maintaining cap assembly is matched with the clamp spring seat in the inner pipe assembly; and when a core of the natural gas hydrate is transferred onto the submarine drilling machine from the bottom of a hole, the pressure-maintaining cap assembly is in inserted connection with the clamp spring seat so as to seal the lower end of the core pipe. The occurrence condition of submarine minerals can be restored to the largest extent through a core sample obtained by the core pressure-maintaining coring drill tool, and the basis is provided for improving the mining technology of the natural gas hydrate.