The invention relates to a tackifier for addition type organosilicon impregnating resin and a preparation method thereof. The molecular formula of the tackifier is (Me2R1SiO0.5)a(MeR2SiO)b(PhSiO1.5)c(R3SiO1.5)d, wherein a, b, c and d represent the mole number of each chain link of the tackifier; and it is at least guaranteed that in R1 and R2, vinyl and hydrogen groups coexist. The tackifier is obtained by hydrolytic condensation of silane monomers containing hydrogen groups, vinyl, phenyl groups and other reactive groups under the effect of a catalyst. The prepared tackifier can remarkably improve high temperature adhesive properties of the addition type organosilicon impregnating resin, the tackifier and the impregnating resin are good in compatibility, the appearance, hardness and other mechanical properties of the resin are not affected after the mixing, and the tackifier has important application to motor and engine insulation impregnation.