Abstract: The development of polymer-based thermally conductive composites with low filling and high thermally conductivity remains a bottleneck problem that needs to be solved. Based on the layer-by-layer hydrogen-bond assembly, the low filling and high thermally conductive BNNS@PDA/PU composites are prepared by the dip coating-hot pressing method, using the porous polyurethane (PU) foams as template, and polydopamine functionalized nitride boron nanosheets (BNNS@PDA) as thermally conductive fillers. The microstructures, thermal conductive properties and thermal stability of BNNS@PDA and BNNS@PDA/PU composites were investigated in detail. The results show that the surface functionalization of BNNS by PDA can make it coat well on the three-dimensional skeleton of porous PU foams. After hot pressing, the highly effective double heat-conduction networks with the PU skeleton as the main heat-conduction network and BNNS@PDA on the surface of PU skeleton as the secondary heat-conduction network are constructed, leading to the decreased interfacial thermal resistance of the thermally conductive composites. When the filling amount of BNNS@PDA is 16.3wt%, the thermal conductivity of BNNS@PDA/PU composites with double heat-conduction networks reaches 0.783 W/(m·K), which is 102.3% higher than that of PU with single heat-conduction network (0.387 W/(m·K)).