Tension-torsional　low　cycle　fatigue　behavior　of　Zr-4　has　been　studied　at　different　strain　ratios　of　φ=-0.5,　-0.63,　-0.7,　-0.8　and　Mises　strain　ranges　of　Δε　eq=0.5%,　0.7%,　0.8%,　1.0%,　1.1%　under　in-phase　loading.　The　biaxial　LCF　lifetimes　of　Zr-4　were　evaluated　using　the　stress　and　strain　damage　parameters,　respectively.　The　former　includes　the　maximum　principal　stress,　COD　stress,　the　maximum　shear　stress　and　Mises　equivalent　stress　parameters,　the　latter　includes　the　maximum　principal　strain,　COD　strain,　the　maximum　shear　strain,　Mises　equivalent　strain,　LE　strain　and　BMK　strain　parameters.　The　stress　parameters　cannot　correctly　describe　the　biaxial　LCF　data　within　a　factor　of　two　scatter　band.　The　testing　data　locate　in　more　damage　side.　However,　the　strain　parameters　can　make　the　biaxial　LCF　lifetimes　to　be　within　a　factor　of　two　scatter　band.　The　Mises　strain,　the　maximum　principal　strain　and　the　maximum　shear　strain　parameters　are　the　most　suitable　strain　parameters　among　the　six　strain　parameters.