Provided is a fixing device for line laser output. The device includes a laser beam expander having: a laser via hole defined in an axial direction thereof; an emitter embedding groove disposed at a laser entry end of the laser via hole, the emitter embedding groove having a peripheral wall coaxial with a peripheral wall of the laser via hole, and a bottom wall perpendicular to the peripheral wall of the laser via hole; and a Powell lens embedding groove disposed at a laser exit end of the laser via hole, the Powell lens embedding groove having a peripheral wall coaxial with the peripheral wall of the laser via hole, and a bottom wall perpendicular to the peripheral wall of the laser via hole.