The phenolic epoxy resin SNE-625 was modified by triptene derivative 3DX, and diaminodiphenyl sulfone (DDS) was used as a curing agent to prepare the resin casting. The heat resistance and dielectric properties of the resin castable body were characterized, and the modification effect of triptene derivatives on phenolic epoxy resin was studied. The physical and chemical properties such as thermal decomposition temperature and melting point, dielectric constant and dielectric loss of triptene derivatives were studied. The experimental results show that the melting point of triptene derivatives is 254 °C, the dielectric constant is 2.5 ~ 3.0 and the dielectric loss is 0.1 ~ 0.4 in the range of 8~16 GHz. With the increase of 3DX addition, the glass transition temperature of SNE-625/DDS casting gradually decreased, and the dielectric constant and dielectric loss showed a decreasing trend. When 5%3DX was added, the glass transition temperature of SNE-625/DDS casting decreased from 195 °C to 178 °C, which was reduced by 8.71%. When 10%3DX is added, the dielectric constant of SNE-625/DDS casting body decreases from 3.49 to 3.36, a decrease of 3.72%, and the dielectric loss decreases from 2.66×10^-2 to 2.55×10^-2, a decrease of 4.13%. The comprehensive results show that 3DX can reduce the dielectric constant and dielectric loss of phenolic epoxy resin SNE-625, and reduce the glass transition temperature of SNE-625.