The invention discloses a continuous processing device and a processing method for an ultra-fine grained metal profile. The device comprises a single-screw extruder, an extrusion rod, an octagonal corner extrusion die, a transverse baffle, a longitudinal baffle, a guide frame, a transverse plug, a longitudinal plug and a forward extrusion forming die, wherein the single-screw extruder is connected with the extrusion rod; a metal billet is horizontally fed into the octagonal corner extrusion die; the single-screw extruder can horizontally extrude the metal billet by the extrusion rod; the octagonal corner extrusion die is connected onto the guide frame; T-shaped extrusion channels which mutually communicate are arranged in the extrusion die and comprise a vertical channel and a horizontal channel; the longitudinal plug is used for plugging the vertical channel; the transverse plug is used for plugging the horizontal channel; the transverse baffle is arranged between the octagonal corner extrusion die and the forward extrusion forming die; and after the transverse baffle is removed, the forward extrusion forming die and the octagonal corner extrusion die are enabled to communicate for subsequent processing. According to the device disclosed by the invention, the large-scale production efficiency and quality are greatly improved, and the production cost and energy consumption are reduced.