With the advancement of communication technology, data transmission volumes continue to increase and processing speeds improve, creating an urgent demand for substrate materials with an ultra-low dielectric constant. Polystyrene (PS) possesses a low dielectric constant due to its non-polar structure. Furthermore, in this study, we incorporate a small amount of mesogenic units into the side chains of the PS polymer significantly reducing its dielectric constant. However, PS materials have low glass transition temperature and poor mechanical durability, that limit its practical industrial applications. To complement the thermal weakness of PS, aramid nanofibers (ANF) are incorporated to form a robust three-dimensional reinforcing network. Thermal analysis revealed that the PStLC-ANF composite maintained excellent thermal stability without deformation. As a result, the composite films achieved both an optimized dielectric constant and excellent durability.