The invention relates to a long-time high-temperature-resistant resin-based composite wave-transmission material and a preparation method thereof. The preparation method comprises the following stepsof (1) preparing a polyimide resin solution; (2) compounding resin and quartz fiber; (3) performing heat treatment under the vacuum condition; (4) performing laying or winding; (5) performing curing and post curing. The composite material prepared by the method has the advantages no micromolecules are released in the curing process; the obtained composite material has low porosity; meanwhile, goodheat resistance grade is realized; good mechanical property and dielectric property are still realized under the high-temperature and long-time conditions; the preparation process is simple; the production efficiency is high; important engineering application values are realized.