an ultralow-index top layer is a prerequisite to preparing high-performance broadband ar coatings. when coupled with hydrophobicity and the abrasion-resistance required in practical applications, the challenge becomes even greater. in this work, a mgf2 ar coating was studied because of the low refractive index of mgf2 and its easily realized strong adhesion through low-temperature heat treatment. in order to obtain an ultralow refractive index and endow the coating with hydrophobicity, we designed several experimental routes and finally adopted mtes/teos co-precursors to direct mgf2 particles to form a honeycomb-like network structure without a template. a final refractive index of 1.15 and good hydrophobicity, with a water contact angle of 1221, were obtained using the mgf2-sio2(ch3) coating. these superior properties were attributed to the incorporation of methyl groups, which not only endowed the coating with hydrophobicity, but also changed the original linear assembly of mgf2 particles to a circular assembly. using this hydrophobic ultralow-index coating as a top layer, a high-performance double-layer ar coating was fabricated with a high average transmittance of 99.43% in the wavelength range of 400-1000 nm, good abrasion-resistance, and damp heat resistance after a low-temperature heat treatment of 250 degrees c. this mgf2 double-layer ar coating may be used in display devices or lenses.