Abstract: In order to investigate the relationship between dielectric properties of quartz fiber/polyimide (KH308) composites and fiber volume fraction of composites, frequency, temperature and water absorption, four kinds of quartz fiber reinforced KH308 composites with different fiber volume fractions were prepared by hot pressing technology. Dielectric constant and dielectric loss of these composites were characterized by high Q resonance cavity method in different conditions. The results show that dielectric constant of quartz fiber/KH308 composites increases with increasing fiber content, and the dielectric loss basically does not vary with fiber content. At 7-18 GHz, dielectric constant and dielectric loss of the composites do not vary with frequency. The dielectric constant increases with temperature slowly, while the dielectric loss decreases with increasing temperature at 25-300℃. Dielectric constant and dielectric loss of the composites increase with water content. Fiber/KH308 composites with low dielectric constant (ε<4) and low dielectric loss (tanδ<0.1), can satisfy the requirements of dielectric properties of the missile radome wave-transparent materials.