Regulating refractive index over a wide range plays a key role in the design and fabrication of broadband antireflective coating in many optical energy-related fields. In this paper, hydrophobic refractive-tunable coating was fabricated from an effective solution mixing method starting from a synthesis solution of silica (SiO2) nanoparticles which was developed for dispersing nanoparticles into dense hexylene-bridged polymethylsiloxane polymer. In the mixing process, the microstructure and chemical structure of hexylene-bridged polymethylsiloxane/SiO2 were analyzed by fourier transform-infrared spectrometer and transmission electron microscope. Specially, the relationship between the microstructure and optical properties was also well investigated. Silica nanoparticles were dispersed homogeneously in polymer matrix modulating the refractive index of composite coating ranging from 1.16 to 1.47. When the composite coating with refractive index of 1.36 was used as the bottom layer and hexamethyldisilazane modified SiO2 coating with refractive index of 1.16 was used as the top layer. Thus-obtained double-layer broadband antireflective coating was fabricated with excellent broadband antireflective performance. In addition, the double-layer broadband silica antireflective coating showed good environmental stability. This work provides an alternative way to prepare a broadband antireflective coating for some applications in energy harvesting and optical devices. © 2020 Elsevier B.V.