The invention provides a great-depth seabed portable electric cutting device which can be loaded onto a 7000-meter manned submersible and conducts cutting and sampling on underwater ore. The device comprises a direct current motor and a reducer, the direct current motor and the reducer are fixed to an output shaft through a coupling and a bearing, and an oil charge cavity is formed in a shell body of a shell. The static sealing design is adopted between a front end cap of the shell and the shell, and one or more O-shaped rubber rings are arranged at the contact part between the front end cap and the shell; a rotating combination sealing ring is arranged at the contact part between a revolving shaft and the front end cap, the double-acting rotating seal is adopted for the rotating combination sealing ring, and the sealing pressure can reach 30 MP; the same static sealing design is adopted at a rear end cap of the shell, and one or more O-shaped rubber rings are arranged at the contact part between the rear end cap and the shell. By means of the device, the problems that existing great-depth underwater rock sampling mechanisms are difficult to sample or load, complex in structure, high in fabrication cost, hard to maintain and the like are solved, and the device has the advantages of being simple in fabrication, high in efficiency, safe and reliable.