Fiber-reinforced composite materials, due to their lightweight, high strength, high modulus, and good fatigue resistance, have been increasingly widely used in fields such as aerospace, rail transportation, automotive, and civil engineering. However, the reinforcing fibers used to manufacture these advanced composites are mostly synthetic fibers, which require a significant amount of energy during production and can have a severe impact on the environment after use. With increasing global attention to environmental protection, it is urgent to develop new technologies to mitigate the environmental impact of fiber-reinforced composite materials. This project aims to replace synthetic fibers with plant fibers from nature to produce fiber-reinforced composites. Compared to synthetic fibers, plant fibers are lighter, greener, and more environmentally friendly. Currently, research and development of resource-friendly green aviation, green vehicles, and green buildings have become a consensus in the international advanced technology field. Plant fibers possess a microstructure with multiple levels and scales that are completely different from traditional synthetic fibers. When combined with resin matrices to form composite materials, they create a unique multi-level and multi-scale interface structure, which poses new challenges and difficulties for the study of mechanical damage failure mechanisms and other mechanical theories in composite materials. Solving these challenges and difficulties is crucial for achieving high performance and multifunctionalization of plant fiber-reinforced composite materials, and for replacing the currently widely used glass fiber-reinforced composite materials. The main findings of this project are as follows: 1. By designing the interface structure of plant fiber-reinforced composite materials, a multi-level and multi-scale mechanical damage failure model is constructed. This development transforms the traditional single micro-scale failure mode of synthetic fiber-reinforced composites into a multi-level structure that includes microscopic, submicroscopic, and even nano-scale levels. Multiscale composite material interface fracture modes have achieved improvements in interface and other mechanical properties. 2. The concept of multi-level, multi-scale interface mechanics design for composites has been proposed, providing a new scientific method for the high performanceization of composites. 3. Through the proposed new concept of multi-level, multi-scale plant fiber reinforced composite material mechanics/acoustics/flame retardancy design, the multifunctionalization of this type of composite material has been realized, enhancing its competitiveness with glass fiber reinforced composites and promising to replace them. This is of significant importance for solving the resource and environmental problems caused by the extensive use of these synthetic fibers, such as non-recyclability and energy consumption. The project has been supported by national key basic research development plans, National Natural Science Foundation, and other funding sources. The author has published 31 SCI papers in renowned journals in the field of composite materials (as of December 31, 2016), and holds 4 authorized patents. The research results have received widespread attention and recognition from peers both domestically and internationally, including academicians of the Canadian Academy of Engineering. Eight representative papers have been cited 357 times in SCI-E. The new concepts proposed for multi-level and multi-scale design of interface fracture damage in composite materials and mechanical/acoustic/flame retardant design have been successfully demonstrated as leading applications in key model tasks such as national aviation and rail transit. These include the cabin interior wall panels developed for the production of the Chinese General Aviation Corporation's Jiaolong 600, the internal structure of Kunming Metro Line 1 trains, and the cockpit interior wall panels and de-icing plate structures of XX military aircraft. The research results have also been recognized by Boeing Company in the United States. It was pointed out that their research work demonstrated the potential of this green material for application in aviation, an area with challenging requirements.