The invention provides a method and a device for hot-rolling forming of a cylindrical gear with the big modulus and the large diameter. The method comprises the following steps: S1, a blank is obtained; S2, the blank is arranged on a blank driving shaft and clamped by a clamping device; S3, the blank is heated by an induction heating device; S4, left and right baffle plates are mounted to two ends of a mold; S5, a driving device drives the mold and the blank to rotate in opposite directions at a certain speed ratio, and meanwhile, the mold is fed radially through a linear driving device; S6, when the center distance between the mold and the blank reaches a predetermined value, radial feeding of the mold is stopped, the mold is rotated continuously for two circles, and then the mold and the blank are rotated reversely for two circles simultaneously and stopped; S7, the clamping device loosens, and the blank is discharged. The device comprises a rack, the blank driving shaft, a mold driving shaft and an electromagnetic induction coil. According to the method and the device, the cylindrical gear is integrally formed by one step through continuous local plastic deformation, the production efficiency is improved, the materials are saved, and the product performance can be enhanced.