Strain　engineering　in　semiconductor　nanostructure　has　been　received　great　attention　because　their　ultra-large　elastic　limit　can　induce　a　broad　tuning　range　of　the　physical　properties.　Here,　we　report　how　the　electrical　transport　properties　of　the　p-type.　＜　100　＞-oriented　Si　nanowires　may　be　tuned　by　bending　strain　and　affected　by　the　plastic　deformation　in　a　transmission　electron　microscope.　These　freestanding　nanowires　were　prepared　from　commercial　silicon-on-insulator　materials　using　the　focusing　ion　beam　technique.　Results　show　that　the　conductivity　of　these　Si　nanowires　is　improved　remarkably　by　bending　strain　when　the　strain　is　lower　than　2%,　while　the　improvement　is　nearly　saturated　when　the　strain　approaches　to　2%.　The　electric　current　will　reduce　a　little　sometimes　when　strain　exceeds　3%,　which　may　result　from　plastic　events.　Our　experimental　results　may　be　helpful　to　Si　strain　engineering.