Abstract: Plant fibers have the advantages of eco-friendliness, lightweight, high strength, sound and heat insulating, and low carbon footprint, etc. These attributes make them highly sought-after for applications in sectors such as automotive, aerospace, construction, packaging, and transportation, particularly when plant fibers are processed into composites with polymers. This paper briefly describes the effects of the types of plant long fibers and extraction methods on their physical properties, and at the same time outlines the effects of plant long fibers on the physical properties of composites when they are used as reinforcement in combination with the fiber orientation distribution, fiber surface modification, composite molding process, and failure modes under tensile loading, as well as summarizes and looks forward to the application of plant long fiber-reinforced biodegradable composites.