Abstract: Nanoporous phenolic resin matrix composites (NPCs) have broad application prospects in new-generation thermal protection systems owing to their advantages of low density, high strength, excellent high-temperature ablation resistance, efficient thermal insulation, and ease of large-scale fabrication. However, under high heat flux environments, the pyrolytic carbon layer of these materials is prone to oxidative damage, which further induces ablation recession and mechanical erosion. In this work, ZrO₂/BN ceramic coatings were constructed on the surface of needled quartz fiber preforms via a brushing process, and carbon nanotubes (CNTs) were introduced to regulate the coating-matrix interface. CNT-toughened ZrO₂/BN ceramic coating-modified NPCs were prepared through a resin impregnation-sol-gel-ambient pressure drying process. The effects of coating loading and CNT content on the ablation resistance of the composites were systematically investigated. The results show that with the increase of ZrO₂/BN coating loading, the ratio of radial to axial thermal conductivity rises from 0.81 to 1.76, significantly enhancing the in-plane heat diffusion capability. Under the oxy-acetylene ablation condition of 2000℃ for 30 s, the mass ablation rate and linear ablation rate of ZB/NPC-0.4 decrease from 20.18 mg/s and 25.3 μm/s (for the uncoated NPC-0.27) to 14.28 mg/s and 14.07 μm/s, corresponding to reductions of 29.2% and 44.4%, respectively. This indicates that the ceramic coatings inhibit the rapid escape of matrix pyrolysis products and surface solid phase loss, and form an effective barrier in the thickness direction, thereby delaying the penetration of flame into the internal fiber/resin skeleton. With the addition of 1 wt.% CNTs, the linear ablation rate of ZBC/NPC-0.4-1 further decreases to 12.32 μm/s, a reduction of 12.4% compared with ZB/NPC-0.4. The ablation surface roughness is reduced by 63.1%, 58.1%, and 66.8% at 1600℃, 1800℃, and 2000℃, respectively, effectively suppressing coating warpage and mechanical erosion. Microstructural analysis reveals that ZrO₂/BN forms a dense polycrystalline ceramic layer at high temperatures, while CNTs promote the stability of the residual carbon network and relieve thermal stress. The synergistic effect of the two significantly improves the surface integrity and ablation resistance of lightweight nanoporous phenolic composites.