The invention relates to a device and a method for assembling axial magnetic flux permanent magnet motors. The device comprises a fixing portion, a lifting portion and a fine adjustment portion, and is characterized in that the fixing portion comprises a bottom plate, a lifting main guide rail and a worktable, and the lifting main guide rail and the worktable are perpendicularly fixed to the upperend of the horizontal bottom plate; the lifting portion comprises a transverse guide rail, the transverse guide rail is horizontally connected onto the lifting main guide rail, the fine adjustment portion comprises a lifting auxiliary guide rail and a rotor disc fixing device, the lifting auxiliary guide rail is vertically connected onto the transverse guide rail, and the rotor disc fixing deviceis connected to the lower end of the lifting auxiliary guide rail and is positioned on the upper side of the worktable. The device and the method have the advantages that most assembling procedures are mechanized, accordingly, the assembling efficiency and the assembling quality of the integral axial magnetic flux permanent magnet motors can be improved, and accumulated errors due to manual assembling can be reduced; unnecessary manual operation can be reduced to a great extent, and the axial magnetic flux permanent magnet motors can be assuredly safely and reliably assembled.