The　thermal　fatigue　and　mechanical　fatigue　are　the　two　main　failure　modes　for　board　level　solder　joint　in　SMT.　The　comparison　investigation　of　thermal　fatigue　and　mechanical　fatigue　behavior　of　solder　joint　are　carried　out　by　experimental　method　in　this　study.　The　surface　mounted　test　PCB　is　used　and　two　kinds　of　solder　materials,　including　SAC305　and　Sn37Pb,　are　considered.　It　is　shown　that　lead-free　solder　joint　(SAC305)　has　a　longer　thermal　fatigue　lifetime,　but　a　shorter　mechanical　fatigue　lifetime　than　traditional　eutectic　lead-tin　solder.　Moreover,　the　inelastic　strain　(including　creep　and　plastic　strain)　evolutions　of　solder　joint　during　thermal　and　mechanical　fatigue　procedure　are　analyzed　by　FEM　individually.　It　shows　that　the　creep　and　plastic　strain　in　mechanical　fatigue　procedure　is　different　from　those　in　thermal　fatigue.