The invention discloses a phosphaphenanthrene structure and vinyl containing-hyperbranched polysiloxane and a preparation method thereof. The preparation method comprises the steps of evenly mixing distilled water with vinyl-containing trialkoxysilane, dropwise adding catalyst slowly under the stirring condition, and increasing temperature to 50-60 DEG C, thus obtaining vinyl-containing hyperbranched polysiloxane; and mixing the vinyl-containing hyperbranched polysiloxane with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, adding initiator and alcohol solvent, increasing temperature to 95-100 DEG C, and carrying out purification, filtering, reduced pressure distillation and vacuum drying after reaction is finished, thus obtaining phosphaphenanthrene structure and vinyl containing-hyperbranched polysiloxane. The phosphaphenanthrene structure and vinyl containing-hyperbranched polysiloxane integrates molecular properties of hyperbranched polysiloxane, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and vinyl, thus having wide application prospects on polymer modification aspect. The preparation method adopted has the advantages of wide applicability and simple operation process.