In　SMT,　it　is　not　easy　to　study　the　failure　process　of　solder　joint　under　thermal-mechanical　coupled　fatigue　loading.　However,　it　is　very　important　for　the　electrical　circuit　working　in　the　thermal　and　vibration　coupled　environment.　In　this　paper,　the　inelastic　strain　evolution　in　lead-free　solder　joint　under　thermal,　mechanical,　thermal-mechanical　coupled　fatigue　loading　was　studied　by　numerical　simulation,　respectively.　And　the　effect　of　amplitude　and　frequency　of　mechanical　fatigue　loading　on　inelastic　strain　in　solder　joint　were　investigated.　It　was　shown　that　under　thermal-mechanical　coupled　fatigue　loading,　there　is　a　large　value　distribution　of　inelastic　strain　near　the　corner　of　the　border　between　the　chip　and　solder　material.　When　the　amplitude　and　frequency　of　mechanical　fatigue　loading　are　both　small,　the　creep　strain　in　solder　joint　is　dominant.　Otherwise,　the　plastic　strain　is　larger　than　creep　strain.