Abstract: The present invention provides a salt of demethyl tramadol, i.e., a compound represented by formula (I) or a solvate thereof, a pharmaceutical composition comprising the compound represented by formula (I) or the solvate thereof, and a use of the compound represented by formula (I) or the solvate thereof or the pharmaceutical composition in the treatment of moderate to severe pain. The compound or pharmaceutical composition of the present invention can stably release a drug having analgesic activity in a body for a long period of time, can be conveniently used by doctors and patients while exerting pharmacological effects, and has good medication compliance.