A track nut with a protective device comprises a nut body and steel balls, and the inner wall of the nut body is provided with at least one transverse half wedged slot; all the transverse half wedgedslots are from shallow to deep in the screwing direction of bolts, and a spring is preinstalled on the deeper side of each transverse half wedged slot; and the shallower side of each transverse half wedged slot is provided with the steel balls. According to the track nut, since a ring deep groove of the nut body is omitted, the nut cost is reduced, and the step of embedding a lock ring in the ringdeep groove is further omitted during installation; and the steel balls are jacked to the shallower end of the transverse half wedged slot all the time under action of the springs, so that the cooperation effect of the steel balls and the bolts is ensured all the time, and the anti-theft function is improved.