Abstract: To systematically investigate the effects of hawthorn incorporation ratio and fermentation duration on the bioactive compounds and antioxidant capacity of Hericium erinaceus-hawthorn solid-state fermentation products, this study employed Hericium erinaceus as the fermentation strain and hawthorn as the medicinal substrate, utilizing solid-state fermentation technology to prepare a series of fermentation products. By analyzing the dynamic changes in total flavonoids (sodium nitrite-aluminium nitrate-sodium hydroxide colourimetric method), total phenolics (Folin-Ciocalteu method), and quercetin (high-performance liquid chromatography) content during fermentation, combined with in vitro and in vivo antioxidant activity evaluations and mathematical modelling, optimal fermentation parameters were determined. Results indicated that the optimal hawthorn incorporation ratio was 20%. Under this condition, the maximum contents of total flavonoids, total phenols, and quercetin in the fermentation products reached 11.74 mg/g (increased by approximately 1.18-fold), 2.74 mg/g (increased by approximately 2.63-fold), and 0.12 mg/g (increased by approximately 11.93-fold), respectively. In vitro antioxidant assays demonstrated that the fermented products exhibited significantly superior scavenging capacity against ABTS⁺, DPPH, and hydroxyl radicals compared to unfermented hawthorn (P<0.05). The highest scavenging rates were observed at 40 days of fermentation, reaching 45.46%, 97.57%, and 47.17%, respectively. Experimental results from the zebrafish oxidative stress model further demonstrated that the fermented products significantly (P<0.05) enhanced the activities of superoxide dismutase (SOD), catalase (CAT), and glutathioneS-transferase (GST) in zebrafish, specifically increasing to 76.50±7.48 U/g, 500.75±36.46 U/g, and 1.66±0.10 U/g, respectively, while effectively reducing oxidized glutathione (GSSG) content, demonstrating robust in vivo antioxidant capacity. Comprehensive evaluation of in vitro and in vivo antioxidant activity revealed that the 40-day fermented product exhibited the most pronounced antioxidant activity. This study confirms that the Hericium erinaceus-hawthorn solid-state fermentation product, prepared with 20% hawthorn incorporation ratio and a 40-day fermentation, represents a novel material rich in bioactive compounds such as flavonoids (particularly quercetin) and phenols, and exhibits excellent antioxidant properties. These findings provide an experimental basis and technical reference for the high-value utilization of medicinal and edible homologous herbal resources.