In　order　to　obtain　the　essence　of　the　nucleation　of　secondary　α　phase　and　its　variants　selection　in　nearly　β-type　Ti-1300　alloy,　the　relationship　of　the　crystal　orientation,　geometric　growth　direction,　quantity,　distribution　of　secondary　α-phase　to　β-phase　grain　boundaries　properties　was　investigated　by　electronic　backscatter　diffraction　(EBSD).　Results　show　that　a　certain　percentage　of　70.5°　special　boundaries　occurs　in　the　alloy　with　solid　solution　for　2　h　at　910　followed　by　water　quenching.　When　the　alloy　is　slowly　cooled　in　the　furnace　at　910,　there　is　a　significant　relationship　between　the　secondary　α　phase　from　β→α　phase　transformation　and　β-phase　grain　boundaries　properties.　The　orientation　of　α　phase　in　common　β/β　grain　boundary　is　not　unique,　which　has　little　effect　on　the　nucleation　of　the　self　grain　boundary　α　phase　variations,　and　there　is　less　self　grain　boundary　α　phase　of　both　sides.　Both　sides　of　the　β　grain　with　special　high　angle　grain　boundaries　(70.5°)　have　the　same　(110)　plane,　which　favors　the　formation　of　the　heterogeneous　nucleation　of　the　self-grain　boundary　α　phase　variants,　and　causes　selective　growth　of　the　α　variant　in　both　sides　of　grain　boundary.　Besides,　special　small-angle　grain　boundaries　(10.5°)　also　cause　α　variant＇s　selective　growth,　but　the　growth　may　only　occur　on　one　side　of　the　grain　boundary,　which　is　different　from　that　of　high-angle　grain　boundaries.　©　2017,　Science　Press.　All　right　reserved.