The invention discloses a disc assembly of a disc transmission device. The disc assembly consists of an inner disc and an outer disc, wherein the inner disc is put in an inner hole of the outer disc, and a lock plate is arranged between the inner disc and the outer disc. The lock plate is placed in a groove formed on the outer disc or the inner disc, a lock plate spring is arranged below the lock plate stored in the groove, the lock plate is provided with teeth matched with teeth on an outer circle of the inner disc or the inner hole of the outer disc, and the lock plate is provided with an unlocking sheet insertion hole. The disc assembly can conveniently change the relative angle of the inner disc and the outer disc, and can conveniently change the unlocking code when the disc assembly is applied to a mechanical coded lock. The transmission device has running reliability; and the safety, reliability and service life of the transmission device are greatly improved.