The invention relates to modified rosin resin and discloses modified rosin tackifying resin as well as a preparation method and application thereof. The preparation method comprises the following steps of: uniformly mixing rosin or rosin derivatives, monoterpene compounds, dicyclopentadiene fractions and catalysts in an autoclave; replacing air in the autoclave by use of nitrogen or carbon dioxide; reacting the mixture at a pressure of 0.2-0.6 Mpa and at 170-290 DEG C for 1 hour to 30 hours; and decompressing after the reaction, and removing low-boiling-point substances, thus obtaining the modified rosin tackifying resin, or adding an antioxidant stabilizer into the mixture at 200-230 DEG C, thus obtaining the modified rosin tackifying resin with higher quality. The softening point of the modified rosin tackifying resin ranges from 80 DEG C to 110 DEG C, the acid value of the tackifying resin is 15-70mg KOH per gram, and the color of the tackifying resin is less than No.6 Ghana color. The modified rosin tackifying resin can be widely applied to the field of tackifiers, coating paint, printing ink and the like, and especially can be applied to the field of metallocene catalysis polyolefin tackifiers.