High　strain　rate　multi-directional　free　forging　(HSMDFF)　is　an　effective　method　to　expand　the　industrial　appli-cation　of　Mg　alloys.　However,　dynamic　recrystallization　(DRX)　and　strengthening　mechanisms　of　the　HSMDFFed　Mg　alloys　have　not　been　understood.　In　this　work,　the　evolution　of　the　LPSO　phase　and　its　roles　on　DRX　of　Mg-8Gd-1Er-1Zn-0.6Zr　(wt.%)　(GEZ811)　alloy　at　various　cumulative　strains　during　the　HSMDFF　process　are　studied,　and　the　corresponding　strengthening　mechanisms　are　analyzed.　As　the　cumulative　strain　increases,　the　lamellar　LPSO　phase　undergoes　four　stages:　kinking,　tearing,　local　breaking,　and　breaking　into　submicron　particles,　while　the　block　LPSO　phase　is　kinked,　torn　and　broken　with　a　long-plate　morphology.　The　LPSO-induced　DRX　(LDRX)　is　dominant　while　the　continuous　dynamic　recrystallization　(CDRX)　is　complementary　for　the　grain　refinement　of　the　HSMDFFed　alloy.　At　??　e　=　2.64,　the　comprehensive　mechanical　performance　of　the　HSMDFFed　GEZ811　alloy　is　optimal,　and　its　tensile　yield　strength　(TYS),　ultimate　tensile　strength　(UTS)　and　elongation　(EL)　are　302.4　MPa,　370.3　MPa　and　11.8%,　respectively.　The　combined　strengthening　effects　of　grain　boundary,　LPSO　phase　and　dislocation　are　responsible　for　the　enhancement　of　mechanical　properties,　in　which　the　grain　boundary　strengthening　is　dominant.　The　present　work　is　beneficial　to　provide　a　low-cost　approach　for　designing　and　fabricating　forged　Mg-RE　alloys　with　advanced　mechanical　performance.