The utility model discloses an emergent clutch of long -range rack and pinion under water, it includes slide mechanism, engaging mechanism, elastic mechanism and locking mechanical system, and slide mechanism includes fixing base and sliding seat, and the sliding seat is horizontal slip and connects in the fixing base, the engaging mechanism includes gear and rack, and wheel and rack is the meshing structure, and the gear is to rotate and connects on the sliding seat, the elastic mechanism includes elastic element, and elastic element sets up between fixing base and sliding seat, during the wheel and rack meshing, elastic element is the compression form, during the wheel and rack separation, elastic element is the nature form, locking mechanical system includes positioning pin, and positioning pin is and inserts the fixing base running through of thread engagement, and positioning pin is the block with the sliding seat and is connected, and positioning pin runs through when inserting fixing base and block connection sliding seat, and the sliding seat drives wheel and rack and is the meshed attitude, the utility model has the advantages of being simple in structure and convenient inoperation, can reliably work under deep water and high irradiation environment.