The invention discloses a method for preparing high-purity dicyclopentadiene (DCPD). The method comprises the steps of adding a diluting agent into crude dicyclopentadiene serving as a raw material during depolymerization, mixing dicyclopentadiene with the diluting agent in a ratio of 0.5-5, and then putting the mixture into a depolymerization rectifying tower, wherein at a normal pressure, the depolymerization temperature is 160-200 DEG C, the reflux ratio is 0.5-5, and the depolymerization time is 1-3 hours; obtaining high-purity cyclopentadiene (CPD) from the top of the tower, putting the cyclopentadiene into a tubular reactor to finally obtain dicyclopentadiene of which the purity is more than 99%, wherein the reaction temperature is 40-120 DEG C, the reaction pressure is 0.1-1.5MPa, and the residence time is 4-10 hours. The method disclosed by the invention has obvious beneficial effects, can reduce polymerization reaction of the crude dicyclopentadiene during depolymerization, and can improve the yield of the dicyclopentadiene; meanwhile, the diluting agent can ensure that impurities including isopropenyl norbornene and the like can be depolymerized, and the purity of dicyclopentadiene is improved, so that the method is particularly suitable for preparing high-purity dicyclopentadiene from the raw material of crude dicyclopentadiene which is obtained through pyrolysis C5 thermal dimerization separation.