Three-dimensional (3D) ordered and robust ceramic skeleton reinforced polymer composites, emerging as a new generation of high-performance thermal management materials, often require complex synthesis processes. While creating an orderly oriented microstructure for ceramic/polymer composites through a biomimetic strategy shows promise, it remains a significant challenge. Herein, inspired by the directional growth structure of wood, a new method that employs in situ ceramicization followed by vacuum impregnation with epoxy resin to achieve the directional Bio-Si3N4/EP composite is proposed. This approach demonstrates that the aligned channels of wood in Si3N4 ceramic enable strong cross-linking with the EP matrix, forming a robust thermally conductive skeleton and restricting thermal expansion at high temperatures. The resulting composite features high thermal conductivity (8.26 W m−1 K−1), a low coefficient of thermal expansion (8 × 10−6 K−1), a low dielectric constant (ε′ < 5) and a high flexural strength of 136 MPa. The enhanced directional heat transfer and effective suppression of thermal expansion are corroborated by infrared thermography and finite element simulations. This work offers a new idea for the straightforward preparation of thermal management materials with integrated properties and oriented microstructure using a biomimetic strategy.