Abstract: Fiber reinforced nanoporous resin composites are a kind of lightweight, good insulation and excellent anti-ablation material, which have a typical heterogeneous structure. Under applied load, the internal nanopores will spawn microcracks. Initiation, aggregation and propagation of these microcracks should play a significant role on the strength, deformation and failure properties of the materials. Herein, nanoporous resin composites with different fiber reinforcements have been prepared using needled quartz fiber mesh (NQF) and needled quartz fiber mesh/fiber cloth (NQCF) respectively. Focusing on the mechanical behavior, the present work studied the tensile strength, tensile modulus, elongation at break, crushing strength, bending strength and the tensile fatigue resistance of composites, and the microstructure evolution of composites have been characterized by CT in situ tensile device. The results show that the mechanical properties of composites are greatly improved by introducing the fiber cloth, and the microcracks firstly initiate in the resin matrix around the edge of the needling areas, while the damage of the resin matrix could be effectively hindered by the fiber structure. Finally, finite element models of nano-porous phenolic resin (NPR) and fiber cloth have been established to analyze the fracture mechanism of materials at different scales.