The invention discloses styrene-butadiene-styrene modified dicyclopentadiene petroleum resin and a preparation method thereof; the styrene-butadiene-styrene modified dicyclopentadiene petroleum resin comprises styrene, butadiene, cyclopentadiene monomer, an inert solvent, an initiator, a terminator, an anti-aging agent, an antioxidant, and a modifier. The preparation method comprises: first, preparing styrene-butadiene-styrene oligomer, weighing cyclopentadiene monomer and an inert solvent, adding them into a reactor, and polymerizing for 4-6 h; second, adding the styrene-butadiene-styrene oligomer, an antioxidant and a modifier, stirring and mixing well, and reacting continuously for 3-5 h; third, purifying the reaction product to obtain the modified dicyclopentadiene petroleum resin. The modified dicyclopentadiene petroleum resin has good adhesiveness and good stability, the compatibility of the petroleum resin with an elastomer material is improved greatly, the applicable range of the modified petroleum resin is widened greatly, and the petroleum resin is well worthy of application.