The invention discloses a preparation method of a modified dicyclopentadiene type cyanate ester resin with low hygroscopicity. Firstly, a modifier with toughening and water-resistant properties is prepared, the modifier has two amino groups, and can react with -OCN groups of a dicyclopentadiene type cyanate ester to carry out front-end polymerization, a soft segment is introduced to achieve the purpose of toughening, and at the same time, the modifier contains a large amount of organosilicone, the organosilicone is introduced by a block bonding manner, the organosilicone has a stable dielectric constant and dielectric loss in a relatively wide temperature range, has relatively high flexibility, and can greatly improve toughness of the cyanate ester, and at the same time, the organosiliconehas good oxidation resistance and low surface energy, the organosilicone is embedded in a space networking resin, and when the resin is cured, silicon atoms are released to the surface of the resin due to low surface energy of the organosilicone, so that the modified cyanate ester resin has good water resistance, and the problem that hygroscopicity is increased during a resin toughing process issolved.