The invention discloses a device and a method for replacing a converter mouth, and relates to the technical field of converter steelmaking in metallurgical industry, which solves the problems of waste of time and labor, long construction cycle and low safety in the temporary built overhauling platform. By adopting the technical scheme, the device for replacing the converter mouth comprises vertical columns and a movable worktable, wherein the top ends of the vertical columns are connected by a platform transverse beam, and a platform cover plate is arranged on the vertical columns; a working transverse beam and a rotary transverse beam are arranged between the vertical columns under the platform cover plate; the movable worktable is arranged on the working transverse beam and the rotary transverse beam, and can be extended or retracted; a counterweight for balancing the worktable is arranged on the platform transverse beam, away from one side of the rotary transverse beam, at the top end of each vertical column, a tool kit is arranged on the platform beam, close to the rotary beam, at the top of each vertical column. According to the device and the method for replacing the converter mouth, the extending length and direction of the movable worktable can be flexibly adjusted, the tilting angle of the converter is adjusted, the auxiliary material carrying time of an operator is shortened, and the quick and safe operation effect is realized.