The　friction　stir　additive　manufacturing　(FSAM)　is　a　new　solid-state　manufacture　technology.　The　re-stirring　process　is　a　remarkable　feature　of　FSAM.　Under　the　action　of　severe　deformation　and　thermal　coupling,　the　grains　of　base　metal　were　crushed　and　refined　layer　by　layer　to　form　a　new　recrystallized　structure,　and　finally　an　additive　forming　component　was　formed.　AZ31　magnesium　alloy　sheet　for　FSAM　process　was　taken　as　the　research　object.　Firstly,　computational　fluid　dynamics　model　of　FSAM　was　established.　The　influence　of　rotation　speed　on　material　rheology,　temperature　field　and　strain　rate　was　studied,　and　compared　with　the　experimental　results.　Secondly,　the　Zener-Hollomon　parameters　of　the　hot　deformation　process　of　the　magnesium　alloy　material　in　the　additive　zone　were　calculated.　Then,　the　Z　parameters　and　the　recrystallized　grain　size　of　in　additive　zone　were　correlated　by　empirical　formula　method.　Finally,　combined　with　the　micro-hardness　test　results　at　1000　r/min,　a　fast　prediction　algorithm　for　the　recrystallized　microstructure　of　the　FSAM　was　proposed.　The　results　indicate　that,　with　the　increase　of　layers,　the　average　grain　size　and　the　average　hardness　in　the　additive　zone　decrease.　With　the　increase　of　the　rotation　speed,　the　strain　rate　and　recrystallized　grain　size　of　the　material　in　the　additive　zone　gradually　increase,　but　the　micro-hardness　shows　a　downward　trend.　©　2020,　Science　Press.　All　right　reserved.