The invention relates to a locking structure of a slotted nut. The locking structure comprises the slotted nut, wherein a threaded hole penetrates through the center of the slotted nut, a connecting shaft is screwed in the threaded hole, a clamping vertical groove is formed in the connecting shaft, a plurality of grooves are formed in the upper surface of the slotted nut along the circumference ofthe outer edge of the threaded hole, one end of the grooves communicates with the threaded hole, connecting threaded holes are formed in the grooves, a locking piece is arranged in the groove which corresponds to the clamping vertical groove in the connecting shaft, a counterbore is formed in the locking piece in the mode of corresponding to the connecting threaded hole, countersunk rivets are screwed in the counterbore and the connecting threaded hole, a projecting part is arranged on one side surface, which faces the threaded hole, of the locking piece, and the projecting part is clamped inthe clamping vertical groove in the connecting shaft. According to the locking structure, the slotted nut can be effectively locked, and the slotted nut can be effectively prevented from loosing; compared with other locking modes of the slotted nut, the locking structure has the advantages of simplicity, convenience and simplicity in matching and processing, and the phenomenon of improper lockingdue to the size of a general locking clamp is avoided.