The various wastes generated by silkworm silk textiles that are no longer in use are increasing, which is causing considerable waste and contamination. This issue has attracted widespread attention in countries that use a lot of silk. Therefore, enhancing the mechanical properties of regenerated silk fibroin (RSF) and enriching the function of silk are important directions to expand the comprehensive utilization of silk products. In this paper, the preparation of RSF/Alsub.2Osub.3 nanoparticles (NPs) hybrid fiber with different Alsub.2Osub.3 NPs contents by wet spinning and its novel performance are reported. It was found that the RSF/Alsub.2Osub.3 NPs hybrid fiber was a multifunctional fiber material with thermal insulation and UV resistance. Natural light tests showed that the temperature rise rate of RSF/Alsub.2Osub.3 NPs hybrid fibers was slower than that of RSF fibers, and the average temperature rose from 29.1 °C to about 35.4 °C in 15 min, while RSF fibers could rise to about 40.1 °C. UV absorption tests showed that the hybrid fiber was resistant to UV radiation. Furthermore, the addition of Alsub.2Osub.3 NPs may improve the mechanical properties of the hybrid fibers. This was because the blending of Alsub.2Osub.3 NPs promoted the self-assembly of β-sheets in the RSF reaction mixture in a dose-dependent manner, which was manifested as the RSF/Alsub.2Osub.3 NPs hybrid fibers had more β-sheets, crystallinity, and a smaller crystal size. In addition, RSF/Alsub.2Osub.3 NPs hybrid fibers had good biocompatibility and durability in micro-alkaline sweat environments. The above performance makes the RSF/Alsub.2Osub.3 NPs hybrid fibers promising candidates for application in heat-insulating and UV-resistant fabrics as well as military clothing.