Abstract: The extensive use of petroleum-based high-molecular-polymer porous materials has led to severe plastic pollution, commonly known as "white pollution". In this study, we developed a green and sustainable mycelium-poplar particle porous composite material by inoculating and cultivating fungal mycelium on poplar particles. After the mycelium grew through the poplar particles, the porous composite material was prepared by air-drying directly. The results indicated that the porous composite material had a low density (0.165 g·cm^-3), high porosity (82.7%), and hydrophobic surface (contact angle: 131.8°). The composite material exhibited excellent mechanical properties (compression strength of 2.39 MPa; Young's modulus of 9.79 MPa). Additionally, the porous composite material had a low thermal conductivity (0.066 W/mK) and an outstanding limited oxygen index (28.4%). This research demonstrates a simple and eco-friendly method for the preparation of mycelium-poplar particle porous composite materials, which holds significant reference value for the high-value utilization of agricultural and forestry biomass.