Fire-sealing gap filler is an environmentally friendly one-component fire-sealing material that can quickly and effectively seal hard-to-reach gaps. It is suitable for joints between curtain walls and floor edges, as well as for gaps with high elongation. It boasts excellent airtightness and watertightness, and has superior elastic deformation capabilities. It won't crack upon use and will expand upon heating during a fire, quickly sealing the gaps left by the combustion of flammable materials. This prevents the spread of fire and smoke through the curtain wall, thereby reducing the extent of fire damage.