Based　on　the　discrete　element　particle　flow　program　PFC3D,　an　undrained　cyclic　triaxial　numerical　model　is　established　to　investigate　the　large　strain　dynamic　characteristics　and　liquefaction　behaviors　of　the　loose　sand　under　stress　amplitude-controlled　and　strain　amplitude-controlled　tests.　The　results　demonstrate　that　the　value　of　micro　parameters　at　the　initial　liquefaction　moment　are　the　same　under　the　two　control　modes.　The　whole　cyclic　loading　process　of　both　loading　control　methods　can　be　divided　into　different　zones　based　on　the　evolution　of　the　micro　parameters.　In　studying　the　movement　state　of　soil　particles　after　initial　liquefaction,　the　strain　amplitude-controlled　test　is　more　comprehensive　to　observe　the　development　process　of　microstructure.　The　peak　value　of　the　damping　ratio　calculated　by　the　typical　symmetrical　hysteresis　loop　method　is　around　0.5%　of　the　deviatoric　strain,　while　is　around　1.0%　of　the　deviatoric　strain　when　considering　the　asymmetry　of　the　stress-strain　hysteresis　loop.　In　stress　amplitude-controlled　tests,　the　phase　transition　and　large　flow-slip　behavior　of　the　loose　sand　will　result　in　an　unclear　peak　of　the　damping　ratio.　In　this　context,　strain　amplitude-controlled　tests　can　be　advantageous　for　the　study　of　loose　sand.