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The modified cyanate ester resin(CE) which can be applied stably in the cryogenic environment was prepared by using phenoxy resin(PKHH) and high purity epoxy resin(EP) through the method of melting prepolymerization. The results show that the curing reaction of CE is accelerated by the addition of PKHH, but the reaction pathways are not changed. It is found that PKHH can improve the ductility by the mechanism of the semi-interpenetrating network (SIPN) in the cured CE networks. Especially, the impact strength value of the CE/EP blends with the content of 10% (mass fraction) PKHH reaches to 18.4 kJ/m2 and the modulus is maintained at about 3.5 GPa at –196 ℃, accordingly the cracks are not observed on the surface of specimens after 20 low-high temperature cycles (–196 to 200 ℃).