The invention belongs to operating mechanisms of overhaul grounding and fault maintenance grounding devices for rail transit systems with rated voltages of DC1800V and DC750V, and discloses an operating mechanism for a rail transit grounding device. A fixed contact blade and a moving contact blade of the grounding device are electrically connected with a contact rail and a running rail of the rail transit respectively. An electric operating mechanism comprises a motor, a driving gear, a conversion gear and a rotary gear, and the conversion gear and the rotary gear are meshed with the driving gear. In an electric operating mode, the conversion gear is meshed with the rotary gear, a manual operation interface is plugged to disable manual operation; in a manual operation mode, the conversion gear is demeshed with the rotary gear, a conversion switch disconnects a motor power source, and meanwhile, the manual operation interface is open, and switching on and off of the moving and fixed contacts can be controlled through a manual rocker; and in a lock mode, the manual operation interface is plugged and the motor power source is disconnected, so that neither manual operation nor electric operation is performed. The operating mechanism for the rail transit grounding device has the advantages of practical and reasonable structural design, elimination of misoperation and high electrical safety.