The　fatigue　fracture　surfaces　of　multiaxial　fatigue　specimens　subjected　to　proportional　and　non-proportional　multiaxial　loadings　were　observed　and　analyzed　by　using　the　scan　electron　microscope.　According　to　the　observed　results　of　the　fatigue　fracture　surfaces,　the　mechanisms　of　fatigue　crack　initiation　and　propagation　were　studied,　and　the　multiaxial　non-proportional　loading　conditions　on　the　appending　hardening　mechanism　were　discussed.　The　results　indicated　that　the　characteristic　of　model　I　fatigue　striations　was　shown　under　proportional　loading,　and　the　fracture　behavior　of　mix　model　I　and　model　II　fatigue　strip　was　shown　under　nonproportional　loading.