SiO2 with gradient refractive index is fabricated via inductively-coupled plasma enhanced chemical vapor phase deposition (ICP-PECVD) technology at room temperature, and the relation between fabrication technology and optical characteristics of SiO2 material is studied. The antireflective characteristic of perovskite cells encapsulated by SiO2 with gradient refractive index is simulated by utilizing the results of ellipsometry analysis. It is found that the perovskite cells show an ultra-low reflectance, which reaches 0.5% at 550 nm. This research provides an alternative way to realize low-temperature encapsulation of perovskite cells with considering optical properties.