The invention provides a technique for quenching along the tooth space of a large tooth ring with hardened tooth surfaces on a medium-frequency basis, particularly for quenching and tempering the tooth surfaces along the tooth space on a medium-frequency induction basis. The technique comprises the following steps: 1), carrying out the tool preparation and on-site installation before quenching and tempering; 2), manufacturing medium-frequency copying inductors heating-quenching along the tooth space and taking the shape similar to the profile of the tooth space, and quenching and back-coolingthe tooth surfaces in a synchronous manner; 3), quenching at intervals of 3 tooth spaces, wherein, one round of the rotation of the parts, that is, 54 teeth, constitutes a working cycle; 4) testing the hardness of a first quenching tooth surface every cycle; and 5), carrying out the tempering heat treatment in a half-tooth ring manner after the surface is quenched. The quenching level of the tooth surfaces of the large tooth ring with the hardened tooth surfaces reaches HRC40-45; the depth of effective hardening layers is larger than or equal to 4mm; the accuracy of the tooth wheel reaches the 988GE level; the tooth ring has the advantages of light and handy structure, large size and service life as long as two times of the ordinary tooth ring with the same specification; and the technique remarkably reduces the weight of the equipment, improves the reliability thereof, and improves the running efficiency thereof.