Absorption　coefficient　α(ν)　and　dielectric　coefficient　Ε(ν)　of　crystal　Cr3+:LiSrAlF6　were　obtained　by　THz　Time　Domain　Spectroscopy　(THz-TDS)　in　the　range　of　0.2-1.2THz.　The　infrared　transmission　spectrum　R(κ)　was　measured　from　6.7cm-1(0.2THz)　to　4000cm-1.　There　is　a　band　of　the　phonon　absorption　in　the　crystal.　The　frequency　ωLO　of　the　longitudinal　optical　phonon　model　LO　is　about　236　THz.　And　the　ωTO　of　the　transverse　optical　phonon　model　TO　is　about　9.42THz.　©IEEE.