Polystyrene (PS) with great flame retardancy has been achieved by addition of polyhedral oligomeric silsesquioxane (POSS). However, the POSS/PS composite showed easy-ignition behavior leading to fire hazard exposed. Aiming to prolong time to ignition (TTI) and improve flame retardancy simultaneously, using non-flammable modifier to decorate POSS is a facile method. Here, two kinds of POSS hybrids (POSS-ILs), denoted as POSS-EVIM and POSS-VIPSP, were synthesized by free radical copolymerization between vinyl POSS and two kinds of ionic liquid, commercial [EVIm]BF4 and Bronsted ionic liquid, respectively. The polystyrene-based composites (POSS-ILs/PS) were prepared by incorporated POSS-ILs into polystyrene. The results of thermal gravimetric analysis test evidenced that both POSS-ILs increased char yield and decreased decomposed rate of composites. Compared with neat PS, the TTI of POSS-ILs/PS was prolonged by 26 s and 21 s, and meanwhile, the fire hazard was decreased due to reduction of peak value of heat release rate (PHRR) and smoke release rate (PSPR) in cone calorimeter test. Scanning electron microscope observed compact residue of POSS-EVIM/PS and honeycombed residual morphology of POSS-VIPSP/PS, and additionally, both of these residual char possessed higher degree of graphitization than that of PS and POSS/PS in Raman spectrum, suggesting good physical barrier for matrix from heat and oxygen. Besides, the flexural strength of both POSS-ILs/PS composites were increased compared with neat PS. Taking the results above mentioned, POSS modified by ionic liquid can be a decent candidate to prolong time to ignition, simultaneously improve fire safety and mechanical properties for polymeric materials.