This　paper　presents　a　warm　ultrasonic　shot　peening　(WUSP)　strengthening　technique　for　the　β-phase　Mg-Li　alloy.　The　impacts　of　ultrasonic　shot　peening　(USP)　and　WUSP　on　the　surface　microstructure　and　microhardness　of　the　β-phase　Mg-Li　alloy　were　investigated　and　contrasted　through　the　utilization　of　X-ray　diffraction,　optical　microscopy,　transmission　electron　microscopy,　and　microhardness　testing.The　experimental　results　demonstrated　that,　in　the　USP　treatment,　when　the　peening　duration　was　set　at　320　seconds,　the　grains　were　refined　to　approximately　91.6　nm,　and　the　surface　hardness　reached　129.37　HV,　which　was　104.37　%　higher　than　that　of　the　original　sample.　After　the　WUSP　treatment,　when　the　temperature　was　maintained　at　100　°C,　the　grains　were　refined　to　around　10.65　nm,　with　an　amorphization　degree　of　6.35　%.　Meanwhile,　the　surface　hardness　attained　154.41　HV,　which　was　19.35　%　higher　than　that　at　room　temperature　and　143.93　%　of　the　original　sample＇s　hardness.Furthermore,　the　mechanism　underlying　the　surface　grain　nanocrystallization　and　partial　amorphization　of　the　β-phase　Mg-Li　alloy　during　USP　and　WUSP　was　explored,　and　the　influence　of　temperature　on　the　microstructure　evolution　mechanism　of　the　β-phase　Mg-Li　alloy　surface　was　analyzed.　It　was　found　that　when　the　temperature　is　100　°C　or　below,　the　＇Temperature＇s　Refinement　Effect＇　prevails,　whereas　when　the　temperature　is　150　°C　or　above,　the　＇Temperature＇s　Coarsening　Effect＇　dominates.　©　2025　Elsevier　B.V.