In　this　paper,　high　temperature　mechanical　fatigue　tests　on　SnAgCu/Cu　solder　joints　were　carried　out　under　three　test　temperatures　(100,　125,　150　A　degrees　C).　Failure　mechanism　was　analyzed　through　observation　of　micro-crack　evolution　and　fracture　morphology.　The　results　show　that　the　deformation　curve　of　solder　joint　under　high　temperature　mechanical　fatigue　tests　can　be　divided　into　three　stages:　strain　hardening　stage,　stable　deformation　stage　and　accelerated　failure　stage,　which　is　similar　to　the　curve　under　creep　test　condition.　In　addition,　the　cyclic　life　decreases　rapidly　with　increasing　temperature.　Deformation　field　in　the　solder　joint　is　non-uniform　and　shear　strain　concentration　occurs　in　solder　close　to　the　intermetallic　compound　(IMC)　layer.　Micro-crack　initiates　at　the　corner　of　the　solder　joint　and　then　tend　to　propagate　along　interface　between　Cu　substrate　and　solder.　The　fracture　morphology　under　three　temperatures　all　exhibits　ductile　fracture　mode　and　the　failure　path　transforms　from　cutting　through　the　top　of　Cu6Sn5　to　propagation　in　solder　matrix　close　to　IMC　layer　with　increasing　temperature.