Continuous　CO2　laser　irradiation　is　exploited　to　realize　nanocrystallization　of　Fe　based　amorphous　alloys　Fe73.5Cu1Nb3Si13.5B9　by　overlapping　of　the　heated　areas,　and　to　get　homogeneous　ultrafine　grains　of　about　10nm　with　a　bcc　alpha-Fe(Si)　structure,　which　is　the　foundation　of　the　excellent　soft　magnetic　property.　X-ray　diffraction　and　transmission　electron　microscopy(TEM)　are　used　for　microstructure　analysis　and　observation,　and　the　results　show　that　irradiation　power　of　71w　similar　to　99w　gives　the　heat　shock　to　the　transformation　from　the　metastable　amorphous　state　to　crystallized　state,　and　proper　time　of　about　20　similar　to　30　seconds　is　necessary　for　optimum　microstructure　and　soft　magnetic　properties.