A top drive mechanism for a drill rod for cutting of delayed coking units in the petroleum refining industry includes a gooseneck connector, a washpipe assembly, an output shaft, and a power mechanism for driving the output shaft to rotate. The output shaft has an integral structure formed by a shaft body and a flange; a step I is disposed on an outer circumferential surface of the output shaft; a support ring is disposed on an end face of the step I; the output shaft mates with the support ring through a key I; a lock nut fixes the support ring onto the end face of the step I; a lower portion of the support ring is provided with a self-aligning thrust roller bearing. The structure has high stability such that the service life of the top drive device is extended and installation and disassembly are easy and fast.
