In　the　SU(2)　singlet　down　type　vectorlike　quark　model,　there　exist　a　tree　level　coupling　zsb　of　b-＞sZ*　and　an　additional　D　quark.　In　the　framework　we　evaluate　the　D　quark　effects　on　B　-＞　Xsγ　by　running　the　Wilson　coefficients　of　the　effective　Hamiltonian　with　the　renormalization　scale　from　mo　to　weak　scale.　Using　the　recent　measurements　for　B　-＞　Xsl+l-,　we　extract　rather　stringent　constraints　on　the　size　and　CP　violating　phase　of　zsb,　and　find　that　the　zero　point　of　the　forward-backward　asymmetry　may　have　large　deviation　from　that　of　the　standard　model　and　is　very　sensitive　to　zsb,　and　therefore,　it　can　be　useful　in　probing　the　new　physics.