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Here, we developed silica aerogel/poly­(vinyl alcohol) (PSG) composites by dispersing silica aerogel (SA) particles in poly­(vinyl alcohol) (PVA) aqueous solution containing glass fibers (GF) and then experiencing directional freezing, freezing–drying, and thermal cross-linking processes. The microstructure, mechanical, thermal, flame retardancy, and hydrophobicity of the composites were investigated. The results show that SA and GF are uniformly distributed in the anisotropic PVA network and SA nanopores are preserved, forming a multistage pore structure with interwoven micrometer-scale PVA and nanoscale SA. The thermal cross-linking at 180 °C results in the obvious reduction of the −OH groups and the production of the −C–O–C group. The composites exhibit excellent mechanical strength under multiple compressive cycles and maintain structural integrity under high pressure (75000 times its own weight). With the low thermal conductivity (35.63 mW/(m·K)) and low density (0.131 g/cm3), the composites show excellent thermal insulation on cold (−75 °C) and hot (150 °C) plates. The composites possess flame retarding properties, with an HRR of 146.48 kW/m2. The water contact angle of up to 135° allows the composites to easily resist stains. This study provides a purely green method to prepare PVA composites with thermal insulation, flame retardant, and hydrophobic properties for industrial applications.