The invention relates to a cable fixing device for a cable trench and a working method thereof. The cable fixing device comprises a vertical fixing mechanism and a horizontal fixing mechanism. The horizontal fixing mechanism comprises a fixing frame, a second rod body, a through groove, a first through hole, a second through hole, an upper pressing mechanism and a lower supporting wheel. A traction rope is movably inserted into the first and second through holes. The upper pressing mechanism and the lower supporting wheel are used for clamping the cable. The horizontal fixing mechanism is provided with a traction mechanism. The traction mechanism comprises a fixing frame and a rotating mechanism. A fixing mechanism is arranged at the joint of the traction rope. The fixing mechanism comprises a rope pressing sleeve, a wire pressing sleeve and a connecting plate fixedly connected with the rope pressing sleeve and the wire pressing sleeve. The connecting plate is inserted at the communication place between the first through hole and the through groove. According to the cable fixing device for the cable trench and the working method thereof, all the trench cover plates of the cable trench do not need to be opened and thus the working efficiency can be improved; and the cables can be laid and fixed in an orderly manner and the cables can be fixed reliably and arranged in an orderlymanner.